A semiconductor device includes an insulating substrate with a conductive pattern including an insulating substrate, a conductive pattern formed on a front surface of the insulating substrate, and a rear heat-sink formed on a back surface of the insulating substrate; a semiconductor chip joined on the conductive pattern through joining material, and leading terminals; and a mold resin exposing a surface of the rear heat-sink and end portions of the leading terminals, and sealing a front surface of the insulating substrate with the conductive pattern, a back surface of the insulating substrate with the conductive pattern, the semiconductor chip, the rear heat-sink excluding the exposed surface thereof, and the leading terminals excluding the end portions thereof. Each of side surfaces of the conductive pattern and the rear heat-sink is formed with a recessed groove, and the recessed grooves are filled with the mold resin.