The yield of a sealing process for a semiconductor device which adopts a flip-chip mounting method is to be improved. In a molding process wherein plural semiconductor chip ICs mounted on a parts mounting surface of a substrate matrix through bump electrodes are to be sealed all together with a sealing resin in a reduced state of the internal pressure of a cavity of a molding apparatus, a clamping pressure at the time of clamping the substrate matrix by both a lower die and an upper die of a molding die is set at a relatively low pressure in an initial stage of injection of the sealing resin and is changed to a relatively high pressure when the sealing resin has covered the semiconductor chip ICs located in a final stage in the resin injecting direction.