To obtain a high thermal conductivity composite material having specific gravity lower than that of the conventional Cu-W or Cu-Mo combined material as heat radiating material, capable of arbitrarily controlling the thermal expansion coefficient from room temp. to 800°C within the range of (9 to 15)ppm/°C, and having thermal conductivity equal to that of the conventional combined material.

Cu, having high thermal conductivity, and silica glass, having low thermal expansion coefficient, are compounded by incorporating at least 80-95wt.% of Cu and 5-20wt.% of silica glass, by which a sintered compact, having ≥120W/mK thermal conductivity and also having thermal expansion characteristics as high as (9 to 15)ppm/°C thermal expansion coefficient from room temp. to 800°C, can be obtained.