As a senior at Torrance High School in Torrance, California, Thompson scored 30 or more points five times and had 20 or more rebounds on six occasions, and led his team to the Division II-A finals in 2006 and quarterfinals in 2005. He averaged 21.5 points, 13.8 rebounds and 4.6 blocked shots as a senior. Thompson wore number 21 for North Carolina. He is the ACC all-time leader in games played at 152. By default he is also the leader in games played at UNC. He has been nicknamed "Smooth" by some of his loyal fan base and is still a beloved fan favorite in Chapel Hill.