A method for manufacturing heat-radiative substrates on which semiconductor devices such as ICs and transistors are mounted and packages using the substrates, wherein a plurality of CuW or CuMo composite materials obtained by the infiltration method or the mixed powder sintering method are joined together with Cu interposed therebetween. Accordingly, the remaining empty holes within the CuW or CuMo materials are filled sufficiently with Cu, allowing high-quality packages having a successful thermal characteristic to be obtained.