To provide a metallic material having high thermal conductivity and small in a thermal expansion coefficient nearly equal to that of a semiconductor device.

This material is provided with a matrix composed of a metallic material and silicon-contg. carbon fibers contained in the matrix. The silicon- contg. carbon fibers contain silicon carbide in such a manner that its content is gradually reduced from the surface layer part side toward the center part. The silicon-contg. carbon fibers to be used here are formed by subjecting pitch series anisotropic carbon fibers, e.g. having 0.1 to 20 μm diameter, 50 to 3,000 μm average fibrous length and 100 to 1,500 W/mK thermal conductivity and heat-treated at 2,000 to 3,000°C to treatment by using gaseous silicon monoxide.