A metallized aluminum substrate for mounting a semiconductor device such as LD or LED is provided and a metallized aluminum nitride substrate having excellent dimensional accuracy and high bonding strength of a wiring pattern. An intermediate material substrate is provided, comprising a sintered aluminum nitride substrate having on its surface a wiring pattern constituted of a conductor layer composed of a composition containing at least high-melting point metal powder, aluminum nitride powder and a sintering auxiliary agent for aluminum nitride is prepared. Then, the intermediate material substrate is fired while the sintered aluminum nitride obtained by sintering using a sintering auxiliary agent of the same kind as that of the sintering auxiliary agent contained in the composition is placed so as to be brought into contact with the conductor layer on the surface of the intermediate material substrate or so as to be present in the vicinity of the conductor layer.