A semiconductor device includes a first GaN layer formed on a substrate, the first GaN layer including a transition metal and an impurity under constant concentration, the impurity forming a deeper energy level in the first GaN layer than energy level formed by the transition metal, a second GaN layer formed on the first GaN layer, the second GaN layer including the transition metal and the impurity under inclined concentration, an inclined direction of the transition metal being same as an inclined direction of the impurity, and an electron supply layer formed on the second GaN layer.