A semiconductor module manufacturing method, including preparing an external terminal that is of a pin shape and that has an outflow prevention portion formed on an outer surface portion thereof, attaching the external terminal to a substrate and electrically connecting the external terminal to the substrate, preparing a transfer molding die including a first mold portion and a second mold portion, which are combinable by attaching a parting surface of the first mold portion to a parting surface of the second mold portion, to thereby form a first cavity and a second cavity that are in communication with each other, combining the first and second mold portions to accommodate the substrate and the external terminal respectively in the first and second cavities, and to sandwich the outflow prevention portion between the first and second mold portions, and encapsulating the substrate by injecting resin into the first cavity.