Thompson was born on June 1, 1988, in Los Angeles, California to Mychal and Julie Thompson. His father, Mychal Thompson, was the first overall pick in the 1978 NBA draft and spent his 14-year career playing for the Portland Trail Blazers, Los Angeles Lakers and San Antonio Spurs in the NBA and Juvecaserta Basket in Italy. Thompson has a younger brother, Klay, who played college basketball at Washington State University before being drafted in the first round of the 2011 NBA draft by the Golden State Warriors. His youngest brother, Trayce, was drafted in the 2nd round of the 2009 MLB Draft by the Chicago White Sox. Thompson played high school basketball at Jesuit High School in Portland, Oregon for two years, before finishing off his high school career at Santa Margarita Catholic High School in Rancho Santa Margarita, California. After high school, he played one year at Stoneridge Prep, located in Simi Valley, California. He averaged 4. 9 points and 3. 1 rebounds per game that season.