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 struggling to a 15-15 record. Watson had three 30-point outings last season, including a 33-point performance in the conference tournament loss to Pepperdine.
California, UNLV and Kansas were among the other schools that showed interest in Watson following his transfer. Watson took just one visit: San Diego State.
Watson, who was ranked as ESPN's No.