PURPOSE: To obtain reliably a resin-molded semiconductor device from a multirow lead frame.

CONSTITUTION: In a resin molding device 30 consisting of top and bottom forces 31 and 32, between which cavities 33 for resin-molding necessary places of a lead frame are formed by clamping the lead frame, a runner 34, which is extended in the direction to intersect orthogonally to respective tie bars 6a to 6c of the lead frame which is clamped between the forces 31 and 32, is recessed in one of junction surfaces which are used as the junction part between the forces 31 and 32, this runner 34 and the respective cavities 33 are connected to each other through gates 35, air escape paths 36a and 36b are respectively recessed in the other junction surface at positions to oppose to the respective tie bars 6a to 6c of the lead frame, which is clamped between the forces 31 and 32, and these paths 36a and 36b are made to connect with the cavities 33.