PURPOSE: To eliminate the production of burrs at the lead frame for a semiconductor device by forming the prescribed position of the lead frame thinner than the other part from both the front and back surfaces.

CONSTITUTION: The thickness of an inner lead 12 is formed to be thinner by the prescribed thickness than the thickness of an outer lead 13 in the lead 13 which is connected to the inner lead 12 of a lead frame 11. In other words, the lead 12 of the frame 11 is formed to be thinner from both front and back surfaces, and a stepped part 14 is formed. When resin is sealed with a lead frame 11 which is thinned at the lead 12, resin which is intruded from a gap between a mold 15 and the lead 12 is stopped by the stepped part 14, thereby eliminating burrs 19 to be generated on both front and back surfaces of the lead 13 of the frame 11.