We present single-electron charging effects in a 150 nm long ambipolar semiconducting single-walled carbon nanotube grown by chemical vapor deposition. The Coulomb blockade model explains all essential features of the data. Due to the ambipolar characteristic, the device can be tuned to be either p or n type by applying a gate voltage. In the p-type region, a single quantum dot is formed and charging behavior is observable up to 150 K. In the n-type region, transport takes place through a coupled dot system and the charging effects can be clearly seen up to room temperature. We also qualitatively discuss the model that explains the formation of two electrostatically coupled dots in the n-type region. (C) 2003 American Vacuum Society.