There is provided a semiconductor device including: a circuit board formed by bonding a first and a second metal plates to both surfaces of an insulating substrate respectively, at least one semiconductor element to be bonded to an external surface of the first metal plate through a first solder, and a radiating base plate to be bonded to an external surface of the second metal plate through a second solder, wherein the first and the second solders are constituted by solder materials of the same type, and a ratio of a sum of thicknesses of the first and the second metal plates to a thickness of the insulating substrate is set in a predetermined range to ensure an endurance to a temperature stress of each of the first and the second solders.