In a semiconductor device, a thinly-molded portion covering a whole of a heat dissipating surface portion of a lead frame and a die pad space filled portion are integrally molded from a second mold resin, because of which adhesion between the thinly-molded portion and lead frame improves owing to the die pad space filled portion adhering to a side surface of the lead frame. Also, as the thinly-molded portion is partially thicker owing to the die pad space filled portion, strength of the thinly-molded portion increases, and a deficiency or cracking is unlikely to occur.