A semiconductor device includes: a substrate; a drift layer which is disposed on the substrate and has a groove; an underlayer which is disposed above the drift layer; a first opening which penetrates the underlayer to reach the drift layer; an electron transit layer and an electron supply layer which are disposed to cover the first opening; a second opening which penetrates the electron supply layer and the electron transit layer to reach the underlayer; a gate electrode which is disposed above the electron supply layer at a position corresponding to a position of the first opening; a source electrode which is disposed to cover the second opening and in contact with the underlayer; and a drain electrode which is disposed on a backside surface of the substrate. A bottom surface of the groove is closer to the substrate than a bottom surface of the first opening.