UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 6-K

Report of Foreign Private Issuer

Pursuant to Rule 13a-16 or 15d-16 under the

Securities Exchange Act of 1934

For the month of October 2025

Commission File Number: 001-41709

 SEALSQ CORP

(Exact Name of Registrant as Specified in Charter)

N/A

(Translation of Registrant’s name into English)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F:

☒ Form 20-F ☐ Form 40-F On October 14, 2025, SEALSQ Corp (“SEAL”) and WeCan Group SA (“WeCan”), a Swiss provider of global compliance infrastructure for regulated institutions, announced a strategic collaboration to develop a Post-Quantum KYC (Know Your Customer) solution, which will aim to secure client data from collection to processing, addressing the growing risk of future decryption by state or malicious actors as quantum computing capabilities evolve.

SEAL’s Chairman, Chief Executive Officer and member of the SEAL board of directors, Carlos Moreira, is a member of the board of directors of WeCan. As of October 14, 2025, Seal holds a 28.3% equity stake in WeCan.

The information contained in this Report on Form 6-K is hereby incorporated by reference into the registration statement on Form F-3 of the Company (File No. 333-286098), as amended, and the registration statement on Form S-8 of the Company (File No. 333-287139), and into the base prospectus and any prospectus supplement outstanding under each of the foregoing registration statements, to the extent not superseded by documents or reports subsequently filed or furnished by the Company under the Securities Act of 1933, as amended, or the Securities Exchange Act of 1934.

SIGNATURES

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, thereunto duly authorized.