S.D. Codified Laws § 23A-20-28
A court may direct that not more than six jurors in addition to the regular jury members be called and impaneled to sit as alternate jurors. Alternate jurors, in the order in which they were called, shall replace jurors who, prior to the time the jury retires to consider its verdict, become or are found to be disqualified, discharged, or unable to perform their duties. Alternate jurors shall be drawn at the same time and in the same manner, shall have the same qualifications, shall be subject to the same examination and challenges, shall take the same oath and shall have the same functions, powers, facilities, and privileges as regular jurors. An alternate juror who does not replace a regular juror shall be discharged after the jury retires to consider its verdict.
SDCL 23A-20-28