PURPOSE: To realize a cooling structure of extremely high cooling efficiency by constituting a multilayer circuit board as the bottom plate of a closely sealed vessel which is equipped with a heat dissipating cap on the upper part and in which refrigerant is injected.

CONSTITUTION: A semiconductor chip 1 is subjected to flip chip bonding to a bump patterned and formed on a ceramic circuit board 3 provided with output pins 7 for being inserted into a mother board 6. A sealing vessel composed of alluminum alloy is so constituted that the ceramic circuit board 3 is used as the bottom plate. Therein refrigerant 8 composed of C6F14 whose boiling point is 56°C is contained, and a heat dissipating cap 10 is arranged above an air gap 9 which is filled with the gas of the refrigerant 8. Said cap 10 is cooled by forced air cooling.