"Competing in the NFL has always been among my highest goals and I believe the time to pursue this opportunity is now," Hansen said in a statement. "This was an extremely difficult decision to make - my time at Cal has been amazing."
Hansen, a former walk-on, emerged as one of the most prolific receivers in the Pac-12 this season, compiling 92 receptions, 1,249 yards, and 11 touchdowns.
The junior, whose career began at Idaho State, elected to turn pro two weeks after Golden Bears coach Sonny Dykes suggested he'd be wise to return for a senior campaign.
"Chad's got a high ceiling. I don't think he's anywhere close to reaching it yet," Dykes told Jeff Faraudo of The Mercury News on Nov. 22. "I think it makes sense for him to come back. He's still a developing guy. He has an opportunity to become one of the elite guys in college football."