S.D. Codified Laws § 49-33-31

If, with respect to any action to be taken by the board of directors or by the stockholders of a corporation, the articles of incorporation require the vote or concurrence of the holders of a greater proportion of the shares, or of any class or series thereof, than required by any section of this title, the provision of the articles of incorporation requiring such greater vote shall not be altered, amended or repealed except by such greater vote.