A method of producing a semiconductor module which includes a resin molded package and a coolant passage is provided. The resin molded package is made up of a thermosetting resin-made mold and a thermoplastic resin-made mold. The resin molded package is formed by making the thermoplastic resin-made mold, placing the thermoplastic resin-made mold and a semiconductor sub-assembly made up of a power semiconductor chip, heat spreaders, terminals, etc., and then forming the thermosetting resin-made mold. Specifically, the thermosetting resin-made mold is made after the thermoplastic resin-made mold, thereby creating a high degree of adhesion of the thermosetting resin-made mold to the thermoplastic resin-made mold before the thermosetting resin-made mold is hardened completely, thereby forming firmly an adhered interface between the thermosetting resin-made mold and the thermoplastic resin-made mold. This minimizes the risk of occurrence of air gaps at the adhered interface and avoids the leakage of the coolant outside the resin molded package.