PURPOSE: To reduce a heat resistance other than the inside of a semiconductor element as far as possible and to enhance a heat-resistant performance by a method wherein a liquid reservoir part of a gasifying coolant liquid is formed in a substrate and a space used to move an evaporated coolant is formed collectively in a hermetically sealed manner so as to be continued to a cooling body.

CONSTITUTION: A gasifying coolant liquid 10 is filled in recessed parts 20 for liquid reservoir in a space 9 hermetically sealed. The coolant liquid 10 is evaporated by heat generated by semiconductor elements 2a, 2b. The vapor of the coolant liquid 10 is spread to the spacer 9, comes into contact with a cooling body 8, is liquefied immediately and is again dropped to the recessed parts 20 for liquid reservoir use. The heat generated by the semiconductor elements 2a, 2b evaporates the coolant liquid 10 by a minimum heat resistance at a shortest distance which is stabilized by brazing a metal to a ceramic. On the other hand, the vapor is liquefied in a part where a temperature on the rear surface of the cooling body 8 is lowest; it is possible to eliminate a heat resistance between the recessed parts 20 in which the coolant liquid 10 is collected and the rear surface of the cooling body 8. In addition, when a slit 9a or a small hole 9b is formed in a fin 8a of the cooling body 8, a heat resistance up to the fin 8a can be made small.