The semiconductor device such as a MOSFET comprises a channel 2, a gate electrode 3, a source or drains and insulating layers 11-13, at least one of which is made of a material capable of conducting heat. The material may be ALN or BN and the gate insulator 4 may also be heat conductive. An assembly of semi conductor devices cooled by a layer of heat conductive material is also described. Air or liquid cooled fins may be attached to the device. <IMAGE>
