Method of manufacturing resin-encapsulated semiconductor device, and lead frame

A resin-encapsulated semiconductor device comprises a semiconductor chip mounted on a die pad. A plurality of leads each having an inner lead and an outer lead are arranged in spaced relation from the die pad with the inner leads facing the die pad. A metal plating layer is formed on top surfaces of the inner leads, and the inner leads are connected by metal wires to the semiconductor chip. An encapsulation resin encapsulates the semiconductor chip, die pad, metal wires and inner leads leaving the outer leads exposed. The outer edge of the metal plating layer coincides with the outer surface of the encapsulation resin and with the outer edge of the metal plating layer.