To provide a semiconductor device that is reduced in cost by further improving the heat radiating property of a box-shaped molded hollow resin body, such as a hollow plastic package, etc., and preventing unnecessary portions from being plated.

In this semiconductor device, an insulating layer 4 is provided on the lower surface of a semiconductor element 2 and a heat sink 3 separated from a lead frame 6 is provided under the insulating layer 4. In addition, the lower surface of the heat sink 3 is exposed from a hollow resin package 1. The heat generated when the semiconductor element 2 is operated is directly discharged to the outside from the heat sink 3 the lower surface of which is exposed from the package 1. In addition, the heat sink 3 is insulated from the element 2 by the insulating layer 4 and, at the same time, by the package 1 which separates the heat sink 3 from the lead frame 4. Consequently, the heat does not exert any adverse influence upon the operation of the semiconductor element 2.