Provided is a resin-encapsulated semiconductor device in which heat dissipation characteristic and mounting strength to a substrate are improved. Heat dissipation outer leads connected to inner leads connected to the four corners of a die pad are exposed to the outside of an encapsulating resin to improve the heat dissipation characteristic. The ends of the heat dissipation outer leads are cut in lead frame pressing, and exterior plating films are formed on the entire surfaces of the heat dissipation outer leads including the ends in exterior plating of the resin-encapsulated semiconductor device, permitting easy formation of solder fillet when the semiconductor device is mounted on a substrate.