A semiconductor device including an insulated circuit board. The insulated circuit board includes an insulating board having an outer edge and a plurality of corners, and a plurality of circuit patterns formed on a front surface of the insulating board. The plurality of circuit patterns have a plurality of outer-edge corners facing the outer edge of the insulating board, among which outer-edge corners corresponding to the corners of the insulating board are smaller in curvature than outer-edge corners that do not correspond to the corners of the insulating board.