Thompson (Sacramento, Calif./Grant) let the rabbit out of the bag Friday, when he announced his decision in a Twitter post: "Talk to my moms... College I'm attending Cal Golden bears... GO BEARS."
The tweet was later removed from his account, but he announced his decision Saturday on national television during the fourth quarter of the U.S. Army All-American Bowl at the Alamodome.
"I really liked all the coaches, and I liked the atmosphere there," Thompson said. "The biggest thing there is the education. I feel like I don't make it to the NFL, I can get a good job with a degree from Cal."
A bruiser in the secondary with legitimate speed, Thompson became the third official Cal commit Saturday, joining four-star receiver Jordan Payton (Westlake Village, Calif./Oaks Christian) and ESPNU 150 defensive tackle Ellis McCarthy (Monrovia, Calif.).
"We just all feel real comfortable there," Thompson said, "and we're going to change the game. A lot of good players are going to Cal. They should be pretty good in the next couple of years."
In high school, Thompson saw time at safety, running back and quarterback.
Thompson originally committed to Cal in the spring but opted to open up the process and took official visits to Arizona State, Cal, Notre Dame, Oregon and Washington. USC also was involved.