Provided is a manufacturing method for a semiconductor device using stamping press working which is capable of securing an island having substantially the same size as that of a related art even when a lead frame thickness is increased. A portion between the island and the inner lead is punched with a punch having a width of equal to or larger than a minimum required plate thickness for stamping press working. A periphery of the island is squeezed from an island back surface. A gap between the island and the inner lead is set to be smaller than a thickness of the lead frame, and at the same time, the thickness of the lead frame in the periphery of the island is set smaller than an original plate thickness of the lead frame, thereby obtaining a required area of the island.