A semiconductor device composed of a Group III nitride semiconductor has the following structure. A substrate has on it an n-type first semiconductor layer, an active layer, and a p-type second semiconductor layer in this order. Two first end faces are formed by cleavage and oppose each other in planar view. Two trenches extend to the two first end faces in the direction orthogonal to the first end faces in planar view. Bottoms of the trenches are positioned at least below the lower surface of the active layer. Second end faces are formed by laser scribing in the direction orthogonal to the first end faces and outside the trenches.