The Van Nuys native will occupy a spot on the Galaxy's developmental roster, and his salary will not count toward the club's salary cap.
"Tristan is an exciting and talented young player who has impressed me and all of our coaches during his time training with the club," Galaxy General Manager and Head Coach Bruce Arena said. "He has many of the attributes which are required in order to become a good player in MLS and has shown the drive and desire to improve all areas of his game. We are excited to have him join the club and look forward to seeing him grow in a Galaxy uniform."
Bowen, a member of the U.S. under-18 and under-20 national team, was the first player to sign the Galaxy Rios program in 2007.
He played in four MLS Reserve Division matches in 2008, making three starts.