An embodiment of a semiconductor device including a silicon carbide layer having a first and a second planes; a first silicon carbide region of first conductivity type in the silicon carbide layer; a second silicon carbide region of second conductivity type in the silicon carbide layer between the first silicon carbide region and the first plane; a third silicon carbide region of the first conductivity type in the silicon carbide layer located between the second silicon carbide region and the first plane; a first electrode located on a side of the first plane; a second electrode located on a side of the second plane; a gate electrode; an aluminum nitride layer containing an aluminum nitride crystal between the second silicon carbide region and the gate electrode; and an insulating layer between the aluminum nitride layer and the gate electrode and having a wider band gap than the aluminum nitride layer.