Tecogen Inc. 美股招股说明书（2025年5月22日版）

TECOGEN INC. Up to 3,800,000 shares of common stock This prospectus supplement dated May 22, 2025, supplements, amends and updates certain information included in the reoffer prospectus,dated June 23, 2022(“reoffer prospectus”), filed by Tecogen Inc., a Delaware corporation(“Tecogen,” “we,” “our,” or “us”), with the Securitiesand Exchange Commission(“SEC”)on June 23, 2022, as part of the Registration Statement on Form S-8. The reoffer prospectus as supplemented bythis supplement relate to the resale of up to 3,800,000 shares(“shares”)of our common stock, $.001 par value per share(“common stock”), which The selling stockholders consist of our current or former employees, directors, officers, and consultants who acquired, or will acquire, theshares of our common stock upon the vesting and exercise of incentive or non-qualified stock options, or upon the grant, vesting and/or exercise ofcertain awards of our common stock issued pursuant to our2022 Stock Incentive Plan(“2022 Plan”). The selling stockholders are, or may bedeemed to be, our“affiliates”and the shares to be reoffered or resold by the selling stockholders are“control securities”under the Securities Act of You should read this supplement in conjunction with the reoffer prospectus. Each selling stockholder that sells shares pursuant to the reofferprospectus as supplemented hereby and any broker or dealer through whom the shares may be resold may be deemed an “underwriter” within themeaning set forth in the Securities Act. In addition, any commissions received by a broker or dealer in connection with resales of the shares may be The common stock offered by the reoffer prospectus as supplemented hereby may be reoffered or resold from time to time in transactionson the NYSE American LLC(“NYSE American”)stock exchange or any other market or exchange on which the shares are quoted or listed, innegotiated transactions, at fixed prices which may be changed, at market prices at the time of sale, at prices related to market prices or negotiatedprices, or by a combination of these methods. All of the proceeds of the resale of the shares offered by the reoffer prospectus as supplemented hereby will be received by the sellingstockholders. However, if options are exercised to purchase shares of our common stock covered by the reoffer prospectus as supplemented hereby,we will receive proceeds from payment of the option exercise price which we expect to use for general working capital purposes. The sellingstockholders will bear all sales commissions and similar expense. All costs associated with the registration of the shares under the Securities Act are Our common stock is currently traded on the NYSE American under the symbol “TGEN.” On May 21, 2025, the closing price of ourcommon stock was $4.36. Investing in our securities involves a high degree of risk. See “Risk Factors” contained in the reoffer prospectus for moreinformation on these risks. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of thesesecurities or passed upon the adequacy or accuracy of the reoffer prospectus, this prospectus supplement, or any further prospectussupplement. Any representation to the contrary is a criminal offense. The information set forth under the caption “Selling Stockholders” in the reoffer prospectus is amended and restated in its entirety as setforth below for the primary purpose of identifying the selling stockholders and the number of our shares of common stock to be reoffered and resoldby each selling stockholder. Terms used herein shall have the meanings set forth in the reoffer prospectus except to the extent set forth herein. The date of this prospectus supplement is May 22, 2025. SELLING STOCKHOLDERS The following selling stockholder table supplements and/or amends the selling stockholder table contained in the reoffer prospectus assupplemented by Supplement No. 1 to add selling stockholders and/or add additional shares that may be reoffered and resold by certain sellingstockholders. The selling stockholder table included in the reoffer prospectus as supplemented and/or amended below sets forth: •the name and principal position of each person who is, or may be deemed, an affiliated selling stockholder, and certain non-affiliated sellingstockholders •the number and percentage of shares of common stock owned beneficially, directly or indirectly, by each selling stockholder before theoffering •the number of shares of common stock to be offered by the selling stockholders pursuant to the reoffer prospectus as amended orsupplemented hereby, and •the number and percentage of shares of common stock to be owned by each selling stockholder following the sale of the shares pursuant tothe reoffer prospectus as supplemented and/or amended by this supplement. We may further amend or supplement the reoffer prospectus from time to time to update the disclosures set forth in the table, below.Because the