A nitride semiconductor device includes a substrate, a first nitride semiconductor layer, a first p-type nitride semiconductor layer and a second nitride semiconductor layer disposed sequentially from below; an electron transport layer and an electron supply layer arranged sequentially from below to cover a first opening and the second nitride semiconductor layer, the first opening penetrating through the second nitride semiconductor layer and the first p-type nitride semiconductor layer; a second p-type nitride semiconductor layer or an insulating layer disposed in a position overlapping with a bottom surface of the first opening; a gate electrode disposed in a position overlapping with the second nitride semiconductor layer; a first source electrode disposed to cover a second opening penetrating through the electron supply layer and the electron transport layer; a drain electrode; and a second source electrode disposed above the second p-type nitride semiconductor layer or the insulating layer.