South dakota constitution
Article III: legislative department
Section 12

No member of the Legislature shall, during the term for which he was elected, be appointed or elected to any civil office in the state which shall have been created, or the emoluments of which shall have been increased during the term for which he was elected, nor shall any member receive any civil appointment from the Governor, the Governor and senate, or from the Legislature during the term for which he shall have been elected, and all such appointments and all votes given for any such members for any such office or appointment shall be void; nor shall any member of the Legislature during the term for which he shall have been elected, or within one year thereafter, be interested, directly or indirectly, in any contract with the state or any county thereof, authorized by any law passed during the term for which he shall have been elected.