Smith was selected by the Miami Heat with the 20th overall pick in the 2007 NBA draft, but was later traded to the Philadelphia 76ers on draft night. As a rookie with the 76ers, Smith averaged 4.5 points and 3.0 rebounds in 76 games. In August 2008, he tore the anterior cruciate ligament in his left knee. He subsequently missed the entire 2008–09 season. Smith returned to action in 2009–10, playing in 56 games and averaging 3.4 points and 2.4 rebounds per game.