A bidirectional switch element includes: a substrate; an AlzGa1-zN layer; an AlbGa1-bN layer; a first source electrode; a first gate electrode; a second gate electrode; a second source electrode; a p-type Alx1Ga1-x1N layer; a p-type Alx2Ga1-x2N layer; an AlyGa1-yN layer; and an AlwGa1-wN layer. The AlzGa1-zN layer is formed over the substrate. The AlbGa1-bN layer is formed on the AlzGa1-zN layer. The AlyGa1-yN layer is interposed between the substrate and the AlzGa1-zN layer. The AlwGa1-wN layer is interposed between the substrate and the AlyGa1-yN layer and has a higher C concentration than the AlyGa1-yN layer.