PURPOSE: To enhance heat dissipation efficiency by bonding a member made of a material having thermal conductivity higher than that of an insulating board to a cavity part for mounting an IC chip and then mounting an IC chip onto the member.

CONSTITUTION: A heat spreader 12 made of a material having high thermal conductivity and having a predetermined area is brazed to the lower part at a cavity part 14 of an IC package body 10 and fitted in place. An IC chip 11 of predetermined size is mounted on the upper surface of the head spreader 12. A heat sink 13 made of a material having high thermal conductivity and having predetermined bonding area is bonded to the bottom face of the IC package body 10 while spaced apart by a predetermined interval A3 from the head spreader 12. With such structure, material cost and machining cost can be reduced and fatigue fracture can be prevented by enhancing the heat dissipation efficiency.