Abstract: A semiconductor device includes: a first semiconductor layer including AlXGa1-XN (0?X?1); a second semiconductor layer provided on the first semiconductor layer, including AlYGa1-YN (0?Y?1, X<Y), and having a larger bandgap than the first semiconductor layer; a source electrode provided on the second semiconductor layer; a drain electrode provided on the second semiconductor layer; and a gate electrode provided on the second semiconductor layer between the source electrode and the drain electrode. A region of the second semiconductor layer below the gate electrode at a depth short of the first semiconductor layer is doped with atoms to be negatively charged in the second semiconductor layer.