The reliability of a photosensor-type semiconductor device is enhanced. The sealing step in a manufacturing process for the semiconductor device is carried out as described below. A molding die having an upper die and a lower die is prepared and a film is arranged between the upper die and the lower die. A lead frame in which first adhesive, a semiconductor chip, second adhesive 11, and a base material are mounted over the upper surface of each tab is arranged between the film and the lower die. The base material has an opening formed therein and the opening is covered with a protective sheet. The semiconductor chip has a light receiving area formed in its main surface. The upper die and the lower die are clamped to cause part of the base material to bite into the film. Thereafter, sealing resin is supplied to between the film and the lower die to form a blanket sealing body. Thus the photosensor-type semiconductor device without resin flash over the light receiving area is obtained.