Del. Code tit. 8 § 344
Any corporation organized under this chapter may become a close corporation under this subchapter by executing, acknowledging and filing, in accordance with § 103 of this title, a certificate of amendment of its certificate of incorporation which shall contain a statement that it elects to become a close corporation, the provisions required by § 342 of this title to appear in the certificate of incorporation of a close corporation, and a heading stating the name of the corporation and that it is a close corporation. Such amendment shall be adopted in accordance with the requirements of § 241 or 242 of this title, except that it must be approved by a vote of the holders of record of at least 2/3 of the shares of each class of stock of the corporation which are outstanding.
8 Del. C. § 344