Heatsink package for flip-chip IC

A semiconductor device which includes a substrate, a semiconductor element mounted on the substrate, a cap having an opening smaller than the external size of the semiconductor element for covering the semiconductor element to provide a hermetic seal, and a heatsink member mounted on the cap covering the opening and making contact with the semiconductor element via the opening. Heat generated by the semiconductor element is conducted directly to the heatsink member. A method of producing the semiconductor device includes mounting the semiconductor element onto the substrate, covering the semiconductor element with a cap which is fixed to the substrate, and mounting the heatsink member on the cap for covering the opening and making contact with the semicondutor element via the opening.