PURPOSE: To enable realization of a sealing method being excellent in mass production properties and having high reliability, by molding a liquid thermosetting sealing material by injecting it into a die heated to a high temperature beforehand.

CONSTITUTION: A thermosetting sealing material kept in a state of liquid at a lower temperature than the one of a molding die is put under pressure and injected into the molding die wherein a semiconductor device is held, and it is molded in the die having a higher temperature than the one of the thermosetting sealing material. kept in the state of liquid. For instance, a semiconductor element prepared by joining a semiconductor chip to a lead frame and by wire-bonding electrodes on the semiconductor chip to lead wires by using Au wires is held in the die heated to 150°C, and then liquid thermosetting epoxy resin heated to 80°C is injected under pressure. By holding the epoxy resin in the die for 120 seconds as it is, it is set thermally and a semiconductor device sealed and molded with the resin is obtained. According to this constitution, occurrence of a disconnection fault in a bonded part of the electrode of the semiconductor device and the wire, a short circuit fault therein due to contact with an adjacent wire, etc. can be prevented and the semiconductor device being excellent in reliability can be obtained.