To prevent a semiconductor device which can be made to be small even though a big-sized chip is used and in which a MOSFET having a low on-resistance can be formed, a semiconductor device according to the invention includes a resin package; at least two main leads that are integrated within the resin package so as to constitute a chip mounting portion; a semiconductor chip mounted on the chip mounting portion; and first and second surface leads each electrically connected to an electrode formed on a surface of the semiconductor chip. The main leads and the first and second surface leads protrude outward along a bottom surface of the resin package, respectively.