A semiconductor device includes a semiconductor substrate provided with an IGBT cell having a collector region and a diode cell having a cathode region, a first defect layer and a second defect layer in a drift region. A region present in the drift region and surrounded by an interface between the IGBT cell and the diode cell orthogonal to a first principal plane, and a plane passing through a boundary between the collector region and the cathode region on a boundary line along an interface between the collector region and the drift region and crossing the first principal plane at an angle of 45 degrees is referred to as a boundary region. The diode cell satisfies a relationship of SD1>S, in which S is an area occupied by the boundary region and SD1 is an area occupied by the diode cell in a surface of the drift region.