Tecogen ends resale registration for unsold shares

Rhea-AI Filing Summary

TECOGEN INC. (TGEN) has filed Post-Effective Amendment No. 3 to its previously effective registration statement to de-register all remaining unsold shares that were earlier registered for resale. The original Form S-3 registration covered 706,147 shares of common stock and was declared effective in 2016, later converted to Form S-1 by post-effective amendments in 2021 after the company voluntarily de-listed its common stock from The NASDAQ Stock Market and de-registered it under Section 12(b) of the Exchange Act. This amendment formally removes any unsold registered shares from registration in accordance with the company’s prior undertakings.

Filing Explained

The August 31 amendment de-registers all shares still unsold under this registration, ending their registered resale status; registration itself does not constitute a sale.

Key Figures

Registered Securities: 706,147 shares of common stock Par value: $0.001 per share Original filing date: July 7, 2016 +5 more

8 metrics

Registered Securities 706,147 shares of common stock Shares originally registered for resale under Form S-3 (File No. 333-212433)

Par value $0.001 per share Par value of TECOGEN INC. common stock registered

Original filing date July 7, 2016 Date the original Form S-3 registration statement was filed

Initial effectiveness date July 18, 2016 Date the registration statement was declared effective by the SEC

Loss of Form S-3 eligibility June 9, 2020 Date TECOGEN INC. ceased to be eligible to use Form S-3

Post-Effective Amendment No. 1 filing date March 12, 2021 Filed as a Form S-1 post-effective amendment

Post-Effective Amendment No. 2 filing date March 19, 2021 Filed as a further Form S-1 post-effective amendment

Declaration of effectiveness for Amendments 1 and 2 March 22, 2021 Date both Form S-1 post-effective amendments were declared effective

Key Terms

Post-Effective Amendment, Registration Statement on Form S-3, Form S-1 Registration Statement, secondary transactions, +2 more

6 terms

Post-Effective Amendment regulatory

"This Post-Effective Amendment No. 3 is being filed to de-register all"

A post-effective amendment is an official update to a securities registration document filed after that document has become effective with regulators; it corrects, adds or replaces information about the securities, the company, or an offering. Investors care because it keeps the legal record current and can change what is being sold or the rights attached to shares — like getting a revised product manual after a launch that may affect value or use.

Registration Statement on Form S-3 regulatory

"pursuant to a Registration Statement on Form S-3 (File No. 333-212433)"

A registration statement on Form S‑3 is a short, standardized filing a qualified public company uses to register new securities with regulators so they can be sold to investors; think of it as a pre-approved, reusable permission slip that speeds up future offerings. It matters to investors because it lets the company raise money more quickly and cheaply — which can fund growth or pay debt — but may also lead to share dilution or change in ownership, so it affects value and liquidity.

Form S-1 Registration Statement regulatory

"Post-Effective Amendment No. 1 to the Registration Statement on a Form S-1"

A Form S-1 registration statement is a comprehensive disclosure document filed with the U.S. Securities and Exchange Commission when a company intends to sell shares to the public, typically for an initial public offering. It contains detailed financial statements, business description, risk factors, management information and intended use of proceeds, and serves as the official source of truth — like a full inspection report and sales brochure combined — that helps investors judge the company's health, risks and valuation before buying shares.

secondary transactions financial

"for the registration of securities to be sold in secondary transactions"

Sales or trades of already-issued shares or stakes between investors rather than new shares created by the company; think of it like selling a used car between private buyers instead of buying a brand-new model from the dealer. These transactions create liquidity and price signals for holders, can change who controls or influences a company, and help investors value shares when primary fundraising is not involved.

General Instruction I.B.3 regulatory

"pursuant to General Instruction I.B.3 of the Form S-3"

de-registration of its shares under Section 12(b) regulatory

"de-registration of its shares under Section 12(b) of the Securities Exchange"

FAQ

What is TECOGEN INC. (TGEN) doing in this Post-Effective Amendment No. 3?

TECOGEN INC. is filing Post-Effective Amendment No. 3 to its registration statement to de-register all unsold shares of common stock that were previously registered for resale under the Securities Act.

How many TECOGEN INC. (TGEN) shares were originally registered under this registration statement?

The registration statement originally covered 706,147 shares of TECOGEN INC. common stock, par value $0.001 per share, registered for resale by selling stockholders.

Why did TECOGEN INC. (TGEN) switch from Form S-3 to Form S-1 for this registration?

TECOGEN INC. filed post-effective amendments on Form S-1 because, on June 9, 2020, it ceased to be eligible to use Form S-3 after voluntarily de-listing its common stock from The NASDAQ Stock Market and de-registering it under Section 12(b) of the Exchange Act.

When did TECOGEN INC. (TGEN) originally file and have this registration statement declared effective?

TECOGEN INC. filed the original Form S-3 registration statement on July 7, 2016, and it was declared effective by the SEC on July 18, 2016.

What prior post-effective amendments did TECOGEN INC. (TGEN) make to this registration?

TECOGEN INC. filed Post-Effective Amendment No. 1 on Form S-1 on March 12, 2021 and Post-Effective Amendment No. 2 on Form S-1 on March 19, 2021; both were declared effective on March 22, 2021.

Who signed the TECOGEN INC. (TGEN) Post-Effective Amendment No. 3?

The amendment was signed on August 31, 2026 on behalf of TECOGEN INC. by Abinand Rangesh, Chief Executive Officer, and also signed by Chief Financial Officer Roger P. Deschenes and the company’s directors.

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Available on EDGAR 08/31/2026 - 05:23 PM Accepted by SEC EDGAR 08/31/2026 - 05:22 PM Learn about SEC filing dates

As filed with the Securities and Exchange Commission on August 31, 2026.

Registration No. 333-212433

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

_______________

POST-EFFECTIVE AMENDMENT NO. 3

TO FORM S-3

ON

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

TECOGEN INC.

(Exact name of registrant as specified in its charter)

Delaware (State or other jurisdiction of incorporation or organization) 04-3536131 (IRS Employer Identification Number)

76 Treble Cove Road, Bldg. 1

North Billerica, MA 01862

(781) 466-6400

(Address, including zip code, and telephone number, including area code,

of registrant’s principal executive offices)

John K. Whiting, IV, Esq. General Counsel Tecogen Inc. 76 Treble Cove Road Building 1 North Billerica, MA 01862 Telephone: (781) 466-6016 (Name, address, including zip code, and telephone number, including area code, of agent for service) Copies of Communications to: Neil R.E. Carr Somertons, PLLC 1025 Connecticut Avenue, N.W., Suite 1000 Washington, D.C. 20036 Telephone: (202) 459-4651

Approximate date of commencement of proposed sale to the public: This Post-Effective Amendment No. 3 is being filed to de-register all of the unsold securities previously registered under this Registration Statement, as amended.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box. ☐

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this form is post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration number of the earlier effective registration statement for the same offering: ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer ☐ Accelerated filer ☐ Non-accelerated filer x

Smaller reporting company x 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 7(a)(2(B) of the Securities Act. ☐

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the Registration Statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

DEREGISTRATION OF UNSOLD SECURITIES

Tecogen Inc., a Delaware corporation (“Registrant”), registered 706,147 shares of common stock, $.001 par value per share (“Registered Securities”), of the Registrant under the Securities Act of 1933, as amended (“Securities Act”), pursuant to a Registration Statement on Form S-3 (File No. 333-212433) (“Registration Statement”) filed with the Securities and Exchange Commission (“SEC”) on July 7, 2016. The Registration Statement, as amended, was declared effective by the SEC on July 18, 2016. On March 12, 2021, the Registrant amended the Registration Statement by the filing of Post-Effective Amendment No. 1 to the Registration Statement on a Form S-1 Registration Statement and, on March 19, 2021, further amended the Registration Statement by the filing of Post-Effective Amendment No. 2 on a Form S-1 Registration Statement (“Post-Effective Amendment Filings”) and such amendments were declared effective by the SEC on March 22, 2021. The Post-Effective Amendment Filings were filed with the SEC because, on June 9, 2020, the Registrant ceased to be eligible to continue to use the Form S-3 for the registration of securities to be sold in secondary transactions under the Securities Act pursuant to General Instruction I.B.3 of the Form S-3 due to the Registrant’s voluntary de-listing of its shares of common stock from trading on The NASDAQ Stock Market and de-registration of its shares under Section 12(b) of the Securities Exchange Act of 1934, as amended.

By filing this Post-Effective Amendment No. 3, the Registrant hereby further amends the Registration Statement, as amended, to remove from registration all Registered Securities that have not been sold by the selling stockholders as of the date hereof and in accordance with the undertakings made by the Registrant in the Registration Statement, as amended. The Registration Statement, as amended, is hereby amended to reflect the de-registration of such unsold Registered Securities.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant has duly caused this Post-Effective Amendment No. 3 to the Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of North Billerica, Commonwealth of Massachusetts, on August 31, 2026.

TECOGEN INC.

By: /s/ Abinand Rangesh

Abinand Rangesh

Chief Executive Officer

(Principal Executive Officer)

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment No. 3 to the Registration Statement has been signed by the following persons in the capacities and on the dates indicated.

Signature			Title			Date
/s/ Abinand Rangesh Abinand Rangesh			Chief Executive Officer and Director (Principal Executive Officer)			August 31, 2026
/s/ Roger P. Deschenes Roger Deschenes			Chief Financial Officer and Accounting Officer (Principal Financial and Accounting Officer)			August 31, 2026
/s/ Angelina M. Galiteva Angelina M. Galiteva			Director and Chairperson			August 31, 2026
/s/ John N. Hatsopoulos John N. Hatsopoulos			Lead Director			August 31, 2026
/s/ Ahmed F. Ghoniem Ahmed F. Ghoniem			Director			August 31, 2026
/s/ Earl R. Lewis, III Earl R. Lewis, III			Director			August 31, 2026
/s/ Susan F. Hirsch Susan F. Hirsch			Director			August 31, 2026
/s/ John M. Albertine John M. Albertine			Director			August 31, 2026