To enhance reliability and production yield of a semiconductor device.

This semiconductor device has a resin-sealed body, a first semiconductor chip 1 and second semiconductor chip 2, each of which is located in the resin-sealed body and has the electrode on its front face, a first lead which extends from the inside to the outside of the resin-sealed body and is electrically connected to the electrode of the first semiconductor chip, and a second lead which extends from the inside to the outside of the resin-sealed body and is electrically connected to the electrode of the second semiconductor chip. After making the resin-sealed body with the first lead frame laid on the second lead frame, the first and second lead frames are welded together, and dam bars are also welded together. When cutting the dam bars, any clearance, in which cutting chips of the upper portion may remain, cannot be made between them by cutting as they are welded together. Thus, cracks in a package, cracks in a semiconductor chip, and bends in a lead resulting from drop and attachment of cutting chips hardly occur.