PURPOSE: To produce the heat radiative substrate which has low thermal expandability and exhibits high heat radiatability by heating a press molding consisting of a low thermally expandable metallic material fiber and a high heat radiative metallic material and injecting a separately melted high heat radiative metallic material thereto.

CONSTITUTION: The fibers of the low thermally expandable metallic fibrous material, such as 'Imvar(R)', and the metallic material having good heat radiatability, such as copper, are mixed and the mixture is disposed in a metallic mold 5. The mixture is press molded by a moving mold 4 to obtain a base material 1. The mixing ratio of the above-mentioned fibers is preferably 50 to 80vol.%. The base material 1 is then allowed to keep the temperature by a heater 2 at the temp. below the m.p. of the metallic material having the good heat radiatability, for example, within a range from 50°C lower than the m.p. of copper till the m.p. of copper in the case of, for example, copper. The separately melted metal 3 of the above-mentioned metallic material having the good heat radiatability, such as copper, is poured and is press injected via the mold 4 to the base material 1. The high heat radiative metallic material is impregnated at a high packing rate into the base material and the heat radiative substrate having both of the low coefft. of thermal expansion and the high heat radiatability is obtd. in this way.