A semiconductor device includes: a compound semiconductor substrate; a buffer layer, a channel layer, and a Schottky junction forming layer sequentially formed on the compound semiconductor substrate, the buffer layer, the channel layer, and the Schottky junction forming layer each being a compound semiconductor; a source electrode and a drain electrode located on the Schottky junction forming layer; and a gate electrode disposed between the source and drain electrodes and forming a Schottky junction with the Schottky junction forming layer. The dopant impurity concentration profile in the channel layer is inversely proportional to the third power of depth into the channel layer from a top surface of the channel layer. The channel layer has fixed sheet dopant impurity concentration, and the top surface of the channel layer has a dopant concentration in a range from 5.0×1017 cm−3 to 2.0×1018 cm−3.