The yield of semiconductor devices is improved. In an upper die of a resin molding die including a pair of the upper die and a lower die, by lengthening the radius of the cross section of an inner peripheral surface of a second corner part facing an injection gate of a cavity more than that of the other corner part, a void contained in a resin in resin injection can be pushed out into an air vent without allowing the void to remain in the second corner part of the cavity. Consequently, the occurrence of the void in the cavity can be prevented and then the occurrence of the appearance defect of the semiconductor device can be prevented.