A semiconductor device includes a radiation plate having a rear surface roughened by a plurality of dents that overlap with each other; a laminated substrate provided on a front surface of the radiation plate and including an insulating plate, a circuit board provided on a front surface of the insulating plate, and a metal plate provided on a rear surface of the insulating plate; a semiconductor chip provided on the circuit board; a radiator; and a heat radiating material retained between the rear surface of the radiation plats and the radiator. The plurality of dents that roughen the rear surface of the radiation plate provides the rear surface with an arithmetic average roughness ranging from 1 μm to 10 μm, and each of the dents has a maximum dent depth ranging from 12 μm to 71.5 μm, and a dent width ranging from 0.17 mm to 0.72 mm.