Filed Pursuant to Rule 424(b)(3)
Registration No. 333-259637

PROSPECTUS SUPPLEMENT NO. 6

(to Prospectus dated October 6, 2021)

GREENIDGE GENERATION HOLDINGS INC.

3,500,000 Shares of

Class A Common Stock

This prospectus supplement further supplements and updates the prospectus dated October 6, 2021 (as may be supplemented or amended from time to time, the “Prospectus”) relating to the resale of 3,500,000 shares of our Class A common stock, $0.0001 par value per share (“Class A common stock”). This prospectus supplement updates and supplements the information in the Prospectus and is not complete without, and may not be delivered or utilized except in combination with, the Prospectus, including any amendments or supplements thereto. This prospectus supplement should be read in conjunction with the Prospectus and if there is any inconsistency between the information in the Prospectus and this prospectus supplement, you should rely on the information in this prospectus supplement.

This prospectus supplement incorporates into the Prospectus the information contained in our attached:

Our Class A common stock is listed on the Nasdaq Global Select Market under the symbol “GREE”. On December 8, 2021, the closing price of our Class A common stock was $17.49.

See the section entitled “Risk Factors” beginning on page 17 of the Prospectus to read about factors you should consider before buying our securities.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying Prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is December 8, 2021.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): December 7, 2021

GREENIDGE GENERATION HOLDINGS INC.

(Exact Name of Registrant as Specified in its Charter)

Registrant’s telephone number, including area code: (315) 536-2359

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 or Rule 12b-2 of the Securities Exchange Act of 1934:

Emerging growth company  ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

On December 7, 2021, Greenidge Generation Holdings Inc. (the “Company”) completed an offering of $17.0 million of the Company’s 8.50% Senior Notes due 2026 (the “Notes”). The underwriters have a 30-day option to purchase up to an additional $2.55 million aggregate principal amount of Notes. The Notes are a further issuance of, rank equally in right of payment with, are fully fungible with, and form a single series for all purposes under the indenture governing the Notes with, the $55.2 million aggregate principal amount of the Company’s 8.50% Senior Notes due 2026 issued by the Company in October 2021.

The Notes were sold pursuant to the Company’s Registration Statement on Form S-1, as amended (File No. 333-261163), which was declared effective by the Securities and Exchange Commission (the “Commission”) on December 2, 2021. The Notes were issued pursuant to the first supplemental indenture (the “First Supplemental Indenture”), dated as of October 13, 2021, between the Company and Wilmington Savings Fund Society, FSB, as trustee (the “Trustee”). The First Supplemental Indenture supplements the indenture entered into by and between the Company and the Trustee, dated as of October 13, 2021 (the “Base Indenture” and, together with the First Supplemental Indenture, the “Indenture”).

The Notes were offered at $24.50 per Note, including accrued interest from October 13, 2021 to, but not including, December 7, 2021, totaling $0.31875 per Note. The Company received net proceeds after discounts and commissions, but before expenses and payment of the structuring fee, of approximately $16.1 million. The Company intends to use the net proceeds from the Offering for general corporate purposes, including funding capital expenditures, future acquisitions, investments and working capital and repaying indebtedness.

The Notes bear interest at the rate of 8.50% per annum. Interest on the Notes is payable quarterly in arrears on January 31, April 30, July 31 and October 31 of each year, commencing January 31, 2022. The Notes will mature on October 31, 2026.

The Company may redeem the Notes for cash in whole or in part at any time (i) on or after October 31, 2023 and prior to October 31, 2024, at a price equal to 102% of their principal amount, plus accrued and unpaid interest to, but excluding, the date of redemption, (ii) on or after October 31, 2024 and prior to October 31, 2025, at a price equal to 101% of their principal amount, plus accrued and unpaid interest to, but excluding, the date of redemption, and (iii) on or after October 31, 2025 and prior to maturity, at a price equal to 100% of their principal amount, plus accrued and unpaid interest to, but excluding, the date of redemption. In addition, the Company may redeem the Notes, in whole, but not in part, at any time at its option, at a redemption price equal to 100.5% of the principal amount plus accrued and unpaid interest to, but not including, the date of redemption, upon the occurrence of certain change of control events. On and after any redemption date, interest will cease to accrue on the redeemed Notes. If the Company is redeeming less than all of the Notes, the Trustee will select the Notes to be redeemed by such method as the Trustee deems fair and appropriate in accordance with methods generally used at the time of selection by fiduciaries in similar circumstances.

The Indenture also contains customary event of default and cure provisions. If an uncured default occurs and is continuing, the Trustee or the holders of not less than 25% in aggregate principal amount of the Notes may declare the Notes to be immediately due and payable.

The Notes are senior unsecured obligations of the Company and rank equal in right of payment with the Company’s existing and future senior unsecured indebtedness.

The foregoing description of the Indenture and the Notes does not purport to be complete and is qualified in its entirety by reference to the full text of the Indenture and the form of Note. Copies of the Base Indenture, the First Supplemental Indenture and the form of Note are attached to this Current Report on Form 8-K as Exhibits 4.1, 4.2 and 4.3, respectively, and are incorporated herein by reference.

The information regarding the Notes, the Indenture and the Promissory Note set forth in Item 1.01 is incorporated herein by reference.

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(d) Exhibits

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Signature(s)

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned, hereunto duly authorized.

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EXHIBIT 4.3

THIS NOTE IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF A DEPOSITARY (AS DEFINED IN THE INDENTURE) OR A NOMINEE THEREOF. THIS GLOBAL SECURITY IS EXCHANGEABLE FOR SECURITIES REGISTERED IN THE NAME OF ANY PERSON OTHER THAN SUCH DEPOSITARY OR ITS NOMINEE ONLY IN LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE AND, UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART FOR SECURITIES IN DEFINITIVE FORM, THIS GLOBAL SECURITY MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY, OR BY A NOMINEE OF THE DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY, OR BY THE DEPOSITARY OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH SUCCESSOR DEPOSITARY.

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), TO THE COMPANY (AS DEFINED BELOW) OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY SECURITY ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

GREENIDGE GENERATION HOLDINGS INC.

8.50% Senior Note due 2026

Greenidge Generation Holdings Inc., a Delaware corporation (hereinafter called the “Company”, which term includes any successor Person under the Indenture referred to below), for value received, hereby promises to pay to Cede & Co., or registered assigns, the principal sum of seventeen million United States Dollars (U.S. $17,000,000) on October 31, 2026 (the “Maturity Date”) and to pay interest thereon from October 13, 2021 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, quarterly on January 31, April 30, July 31 and October 31 in each year and on the Maturity Date (each an “Interest Payment Date”), beginning January 31, 2022 at the rate of 8.50% per annum, until the principal hereof is paid or duly made available for payment. The interest so payable and punctually paid or duly provided for on any Interest Payment Date shall, as provided in such Indenture, be paid to the Person in whose name this Note (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be the January 15, April 15, July 15 or October 15 (whether or not a Business Day), as the case may be, preceding such Interest Payment Date, and the October 15 immediately preceding the Maturity Date. Any such interest which is payable, but is not punctually paid or duly provided for, on any Interest Payment Date shall forthwith cease to be payable to the Holder hereof on the relevant Regular Record Date by virtue of having been such Holder, and may be paid to the Person in whose name this Note (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of the Notes not less than 10 days prior to such Special Record Date, or may be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Notes may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture.

The amount of interest payable for any interest period, including interest payable for any partial interest period, will be computed on the basis of a 360-day year comprised of twelve 30-day months. If an interest payment date falls on a non-Business Day, the applicable interest payment will be made on the next Business Day and no additional interest will accrue as a result of such delayed payment.

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Payment of the principal of (and premium, if any) and the interest on this Note shall be made at the designated office of the Trustee (as defined below) at WSFS Bank Center, 500 Delaware Avenue, 11^th Floor, Wilmington, Delaware 19801, in such currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided, however, for so long as the Notes are represented in global form by one or more Global Securities, all payments of principal (and premium, if any) and interest shall be made by wire transfer of immediately available funds to the Depositary or its nominee, as the case may be, as the registered owner of the Global Security representing such Notes. In the event that definitive Notes shall have been issued, all payments of principal (and premium, if any) and interest shall be made by wire transfer of immediately available funds to the accounts of the registered Holders thereof; provided, that the Company may at its option pay interest by check to the registered address of each Holder of a definitive Note.

This Note is one of the duly authorized series of Securities of the Company, designated as the Company’s “8.50% Senior Notes due 2026”, initially limited to an aggregate principal amount of $17,000,000 all issued or to be issued under and pursuant to an Indenture (the “Base Indenture”), dated as of October 13, 2021, between the Company and Wilmington Savings Fund Society, FSB, as trustee (hereinafter referred to as the “Trustee”), as supplemented by the First Supplemental Indenture thereto, dated as of October 13, 2021 (the “First Supplemental Indenture,” and, together with the Base Indenture, the “Indenture”). Reference is hereby made to the Indenture for a description of the respective rights, limitation of rights, obligations, duties and immunities thereunder of the Trustee, the Company and the Holders of the Notes.

The Notes may not be redeemed prior to the Maturity Date, except as described in Article 3 of the First Supplemental Indenture.

The Notes are not subject to any sinking fund.

If an Event of Default with respect to the Notes shall occur and be continuing, the principal of the Notes may be declared due and payable in the manner and with the effect provided in the Indenture.

The Indenture permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Company and the rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Company and the Trustee with the consent of the Holders of not less than a majority in aggregate principal amount of the Securities at the time Outstanding of each series affected thereby. The Indenture also contains provisions permitting the Holders of specified percentages in aggregate principal amount of the Securities of any series at the time Outstanding, on behalf of the Holders of all Securities of such series, to waive certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Note shall be conclusive and binding upon such Holder and upon all future Holders of this Note and of any Note issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Note.

No reference herein to the Indenture and no provision of this Note or of the Indenture shall alter or impair the right of the Holder of this Note, which is absolute and unconditional, to receive payment of the principal of and interest on this Note at the times herein and in the Indenture prescribed and to institute suit for the enforcement of any such payment unless the Holder of this Note shall have consented to the impairment of such right.

As provided in the Indenture and subject to certain limitations set forth therein, the transfer of this Note may be registered in the Security register, upon surrender of this Note for registration of transfer at the office or agency of the Company in any place where the principal of (and premium, if any) and interest on this Note are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Security Registrar duly executed by, the Holder hereof or by his attorney duly authorized in writing, and thereupon one or more new Notes of this series and of any authorized denominations and of a like aggregate principal amount and tenor, shall be issued to the designated transferee or transferees.

The Notes are issuable only in registered form without coupons in minimum denominations of $25.00 and integral multiples of $25.00 in excess thereof. Subject to certain limitations therein set forth in the Indenture and in this Note, the Notes are exchangeable for a like aggregate principal amount of Notes of this series in different authorized denominations, as requested by the Holders surrendering the same.

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No service charge shall be made for any such registration of transfer or for exchange of this Note, but the Company or the Trustee may require payment of a sum sufficient to cover any tax or other governmental charge that may be imposed in connection with any registration of transfer or exchange of a Note, other than in certain cases provided in the Indenture.

Prior to due presentment of this Note for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee may treat the Person in whose name this Note is registered as the owner hereof for all purposes, whether or not this Note be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary.

The Indenture contains provisions whereby (i) the Company may be discharged from its obligations with respect to the Notes (subject to certain exceptions) or (ii) the Company may be released from its obligations under specified covenants and agreements in the Indenture, in each case if the Company irrevocably deposits with the Trustee money or U.S. Government Obligations sufficient to pay and discharge the entire indebtedness on all Notes of this series, and satisfies certain other conditions, all as more fully provided in the Indenture.

This Note shall be governed by and construed in accordance with the laws of the State of New York.

All terms used in this Note which are defined in the Indenture shall have the meanings assigned to them in the Indenture.

Unless the certificate of authentication hereon has been executed by or on behalf of the Trustee under the Indenture by the manual signature (which may be scanned, photocopied or faxed or otherwise signed electronically (including by DocuSign or Adobe Sign)) of one of its authorized signatories, this Note shall not be entitled to any benefits under the Indenture or be valid or obligatory for any purpose.

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IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed as of the date first written above.

Signature Page to Greenidge Generation Holdings Inc. Global Note

TRUSTEE’S CERTIFICATE OF AUTHENTICATION

This is one of the Securities of the series designated therein referred to in the within-mentioned Indenture as of the date first written above.

Authentication Certificate to Greenidge Generation Holdings Inc. Global Note

ABBREVIATIONS

The following abbreviations, when used in the inscription on the face of this instrument, shall be construed as though they were written out in full according to applicable laws or regulations.

Additional abbreviations may also be used though not in the above list.

FORM OF ASSIGNMENT

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto

(Please insert Assignee’s legal name)

(Please insert Social Security or other identifying number of Assignee)

(Please print or typewrite name and address including postal zip code of Assignee)

the within Note of GREENIDGE GENERATION HOLDINGS INC. and does hereby irrevocably constitute and appoint attorney to transfer the said Note on the books of the Company, with full power of substitution in the premises.

Dated:

[NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within instrument in every particular, without alteration or enlargement or any change whatever.]