A semiconductor device includes: a buffer layer formed over a substrate; a first semiconductor layer formed over the buffer layer by using a compound semiconductor; a second semiconductor layer formed over the first semiconductor layer by using a compound semiconductor; and a gate electrode, a source electrode, and a drain electrode formed over the second semiconductor layer, wherein the first semiconductor layer contains an impurity element serving as an acceptor and an impurity element serving as a donor; and in the first semiconductor layer, an acceptor concentration of the impurity element serving as the acceptor is greater than a donor concentration of the impurity element serving as the donor; and the donor concentration is greater-than over equal to 5×1016 cm−3.