ClearSign Technologies Corp

S-11 tm2523037d1_s1.htm FORM S-1

As filed with the Securities and Exchange Commission on August 12, 2025

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

CLEARSIGN TECHNOLOGIES CORPORATION

(Exact name of registrant as specified in its charter)

8023 East 63 rd Place, Suite 101

Tulsa, Oklahoma 74133

(206) 673-4848

(Address, including zip code, and telephone number,

including area code, of principal executive offices)

Colin James Deller

Chief Executive Officer

ClearSign Technologies Corporation

8023 East 63 rd Place, Suite 101

Tulsa, Oklahoma 74133

(206) 673-4848

(Address, including zip code, and telephone number,

including area code, of agent for service)

Copies to:

Blake Baron, Esq.

Gabriel Miranda, Esq.

Mitchell Silberberg & Knupp LLP

437 Madison Avenue

New York, New York 10022

Phone: (212) 509-3900

Approximate date of commencement of proposed sale to the public: From time to time after the effective date of this registration statement.

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. x

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) 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 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 a 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, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 under the Securities Exchange Act of 1934. (Check one):

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 that specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

EXPLANATORY NOTE

The shares of common stock registered hereunder consists of shares of common stock issuable upon the exercise of certain redeemable warrants, or the Warrants, to purchase an aggregate of 5,267,222 shares of common stock, par value $0.0001 per share, at an exercise price of $1.05 per share, which Warrants were previously issued in connection with our underwritten public offering completed on April 23, 2024, and the subsequent exercise of the over-allotment option by the underwriters in full. The Warrants are exercisable immediately upon issuance, expire five years after the date of issuance and are redeemable by us, subject to certain market based criteria. The Warrants were issued and sold pursuant to our previous “shelf” registration statement on Form S-3 (File No. 333-265967), or the Prior Registration Statement, that was declared effective on August 12, 2022 and which will expire on August 12, 2025 pursuant to Rule 415(a)(5) under the Securities Act of 1933, as amended.

We are filing this new Registration Statement on Form S-1 for the sole purpose of ensuring that an effective Registration Statement covers the exercise of the outstanding Warrants. In accordance with Securities and Exchange Commission, or the SEC, rules, we may continue to offer and sell securities being registered hereunder during the grace period afforded by Rule 415(a)(5). Pursuant to Rule 415(a)(6), the offering of the unsold securities registered under the Prior Registration Statement will be deemed terminated as of the effective date of this Registration Statement. If we sell any securities being registered hereunder during the grace period, we will identify in a pre-effective amendment to this Registration Statement the new amount of securities to be carried forward to this Registration Statement in reliance upon Rule 415(a)(6).

The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED AUGUST 12, 2025

PRELIMINARY PROSPECTUS

5,267,222 Shares of Common Stock Underlying the Warrants

This prospectus relates to the issuance of up to 5,267,222 shares of our common stock, par value $0.0001 per share, or the common stock, available for issuance upon the exercise of 5,267,222 redeemable warrants, or the Warrants, previously issued as part of our public offering of shares of common stock and accompanying Warrants, at the rate of one Warrants for every one share of common stock, that was completed on April 23, 2024.

Each Warrant has an initial exercise price of $1.05 per share, subject to adjustments, and may only be exercised in cash at the election of the holder at any time beginning on April 23, 2024, the date of issuance, and from time to time thereafter, through and including the fifth anniversary of the issuance date. The Warrants are redeemable by us from time to time, subject to certain market based criteria. Holders of the Warrants are not able to exercise their Warrants on a cashless basis. See “Description of Securities Being Registered” in this prospectus for additional information.

We may receive up to $5.5 million upon the exercise of the Warrants, if and when the warrant holders elect to exercise such Warrants. We will not receive any proceeds from the sale of the underlying common stock by the holders of the Warrants. Any amounts received from such exercises will be used for working capital, research and development, marketing and sales, and general corporate purposes. All costs and expenses incurred in connection with the registration of the offering made hereby will be paid by us. The registration of these shares of common stock does not necessarily mean that any holder of a Warrant will exercise such Warrant or that the underlying shares of common stock will be offered or sold by such holder.

Our common stock is listed on the Nasdaq Capital Market, or Nasdaq, under the symbol “CLIR”. On August 11, 2025, the last reported sale price of our common stock on Nasdaq was $0.54.

You should read this prospectus, together with additional information described under the headings “Information Incorporated by Reference” and “Where You Can Find More Information,” carefully before you invest in any of our securities.

Investing in our common stock involves a high degree of risk. See “Risk Factors” beginning on page 10 of this prospectus and other filings we make with the Securities and Exchange Commission from time to time, which are incorporated by reference herein in their entirety, together with other information in this prospectus and the information incorporated by reference herein.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities, or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is , 2025

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