According to one embodiment, a semiconductor device includes a substrate, a first semiconductor region, a second semiconductor region, a first electrode, a first electrode and a conducting section. The substrate includes a conductive region and has a first surface. The first semiconductor region is provided on the first surface side of the substrate and includes AlXGa1-XN (0≦X≦1). The second semiconductor region is provided on a side opposite to the substrate of the first semiconductor region and includes AlYGa1-YN (0≦Y≦1, X≦Y). The first electrode is provided on a side opposite to the first semiconductor region of the second semiconductor region and ohmically connects to the second semiconductor region. The conducting section electrically connects between the first electrode and the conductive region.