According to one embodiment, a semiconductor device includes a first electrode, a second electrode, a first semiconductor layer, and a second semiconductor layer. The second electrode is separated from the first electrode in a first direction. The first semiconductor layer includes n-type SiC, is provided between the first electrode and the second electrode, and is electrically connected to the first electrode. The second semiconductor layer contacts the first semiconductor layer and the second electrode, is provided between the first semiconductor layer and the second electrode, and includes n-type AlxGa1-xN (0.5≤x≤1). A thickness of the second semiconductor layer is not less than 10 nm and not more than 1 μm.