PURPOSE: To increase the heat dissipation efficiency of a semiconductor device constituting by using a cavity-up type ceramic package PGA, and realize a low profile mounting.

CONSTITUTION: The title device is constituted of the following; a package 1 made of ceramic, a chip 2 mounted in a cavity 1a formed at the central part of the upper surface of said package 1, and a plurality of lead pins 3 planted on the periphery of the lower surface. A heat dissipating means 4 is installed at the central part of the lower surface of the package 1, so as to be capable of thermal conduction. When said semiconductor device is mounted on a printed board 5, it is mounted in the manner in which the heat dissipating means 4 is inserted into a relief hole 5a bored in the printed board 5.