A semiconductor device having high output and a method of manufacturing the same are disclosed in which external resistance is reduced and radiating performance is improved. A MOSFET (70) comprises a plurality of inner leads electrically connected to a surface electrode of a semiconductor pellet having a field effect transistor on a principal surface thereof, a connecting portion for electrically connecting the surface electrode of the semiconductor pellet and the inner leads, a resin encapsulant (29) formed by encapsulating the semiconductor pellet with resin, a plurality of outer leads (37), (38) protruding in parallel from the same lateral surface of the resin encapsulant (29) and a header (28) bonded to a back surface of the semiconductor pellet and having a header protruding portion (28c) protruding from a lateral surface of the resin encapsulant (29) opposite to the lateral surface from which the outer leads protrude, wherein the header (28) has an exposed surface (28b) exposed from the resin encapsulant (29); the outer leads (37), (38) are bent; and the exposed of the outer leads (37), (38) are provided at substantially the same height.