Functionally gradient material and its use in a semiconductor circuit substrate

A functionally gradient member comprises, in an integrated manner, a ceramic part composition layer having desired insulation performance and thermal conductivity, a metal part composition layer having desired thermal conductivity and electric conductivity, and a composite composition layer disposed at a boundary portion between the ceramic part composition layer and the metal part composition layer and having its composition and physical properties which are gradually changed. Accordingly, the metal and the ceramic are integrated into one unit without providing any joining section to provide the functionally gradient member having high joining reliability and having high thermal conductivity.