A resin-sealed semiconductor device includes a semiconductor chip including a silicon substrate; a die pad on which the semiconductor chip is secured via a solder layer; a sealing resin layer sealing the semiconductor chip; and lead terminals connected electrically with the semiconductor chip. One end portion of the lead terminals is covered by the sealing resin layer. The die pad and the lead terminals are formed of copper and a copper alloy, and the die pad is formed with a thickness larger than a thickness of the lead terminals, which is a thickness of 0.25 mm or more.