He made the announcement on Sunday via Periscope.
Watson, a 6-foot-1 guard from El Camino High School (California), averaged 20.3 points and 4.9 rebounds as a sophomore for the Dons. He earned first-team all-West Coast Conference honors, despite San Francisco's struggling to a 15-15 record. Watson had three 30-point outings last season, including a 33-point performance in a conference tournament loss to Pepperdine.
Watson, who was ranked ESPN's No. 4 available transfer, will sit out the 2016-17 season before having two years of eligibility with San Diego State.