Gibson declared for the 2009 NBA draft, and was selected 26th overall by the Chicago Bulls. Along with fellow draft pick James Johnson, he signed with the Bulls in July 2009. Gibson was the starting power forward for most of his rookie season with the Bulls and impressed many people with his high energy and good defense. During the All-Star Weekend, Gibson played in the Rookie Challenge, where the Rookie team won for the first time since 2002. The Bulls made the playoffs, securing the 8th seed in the Eastern Conference. Gibson averaged 7.6 points per game and 7.0 rebounds while the Bulls lost to the Cleveland Cavaliers in the first round. At the end of his first season, he was selected to the NBA All-Rookie First Team.