A semiconductor device comprises a semiconductor chip mounted on an island, and a plurality of leads spaced form the island and connected by wires to the semiconductor chip. An insulating film encapsulates the island, the semiconductor chip, the wires and the leads, and the insulating resin has a concave portion that is in contact with the leads. Each lead has a bottom surface exposed from the insulating resin, and the concave portion of the insulating resin exposes side surfaces which surround the bottom surface of each of the leads located under a bottom surface of the insulating resin. When the semiconductor device is soldered to a circuit board, the concave portion prevents contact between the solder and the insulating resin and improves self-alignment of the semiconductor device on the circuit board.