Mitchell didn't hire an agent, so he retained his college eligibility.
He was named first-team All-Mountain West last season, when SDSU went 30-2, won the MWC regular-season title and would have been a No. 1 or 2 seed in the NCAA tournament, which was canceled due to the coronavirus pandemic.
He is ranked 27th on the school's all-time scoring list with 1,085 points.
Mitchell said Friday that he made his decision after speaking with his family and coaching staff.
Besides completing his degree, "I am excited to join my teammates and for the opportunity to lead our quest for another Mountain West championship, and potential return to the NCAA tournament," he said.
Coach Brian Dutcher said it was important for Mitchell to meet with NBA teams and hear their evaluations.
"As we focus on earning another Mountain West championship in 2020-21, this experience can only be a positive for Matt and the Aztecs," Dutcher said.
Mitchell started last season as the sixth man but moved into the starting lineup after Nathan Mensah was sidelined with a respiratory ailment.