S.D. Codified Laws § 51A-6A-26
In accordance with normal business considerations and upon approval of owners owning two-thirds of the voting stock or ownership units of the trust company, the trust company may issue convertible or nonconvertible capital notes or debentures in such amounts pursuant to terms and conditions as approved by the director. However, the principal amount of capital notes or debentures outstanding at any time may not exceed an amount equal to one hundred percent of the trust company's paid-in capital stock or ownership units plus fifty percent of the amount of its unimpaired surplus fund. Capital notes or debentures that are by their terms expressly subordinated to the prior payment in full of all liabilities of the trust company are part of the unimpaired capital funds of the trust company.
SDCL 51A-6A-26