A semiconductor device of an embodiment includes a first electrode, a second electrode, a silicon carbide layer between the first electrode and the second electrode, and the silicon carbide layer having a first plane and a second plane, the silicon carbide layer including a first trench, p-type first silicon carbide regions and n-type second silicon carbide regions alternately disposed, a p-type third silicon carbide region between the second silicon carbide region and the first plane, and an n-type fourth silicon carbide region between the third silicon carbide region and the first plane, and a p-type fifth silicon carbide region between the first silicon carbide region and the first trench, a gate electrode in the first trench, and a gate insulating layer. The length of the first silicon carbide region perpendicular to the first plane is longer than a depth of the first trench.