Abstract: The present invention produces the following substrate and the following process for producing the substrate. A substrate obtained by filling through holes in a sintered product of aluminum nitride with an electrically conducting layer, wherein said sintered product of aluminum nitride has a thermal conductivity of not smaller than 190 W/mK, and the adhesion strength between said sintered product of aluminum nitride and said electrically conducting layer is not smaller than 5.0 kg/mm2.

Abstract: The present invention prodices the following substrate and the following process for producing the substrate. A substrate obtained by filling through holes in a sintered product of aluminum nitride with an electrically conducting layer, wherein said sintered product of aluminum nitride has a thermal conductivity of not smaller than 190 W/mK, and the adhesion strength between said sintered product of aluminum nitride and said electrically conducting layer is not smaller than 5.0 kg/mm2.

Abstract: A submount including:an insulating substrate having therein a throughhole filled with a sintered metal powder, andan electroconductive layer formed on each of the two opposing surfaces of the insulating substrate, wherein the sintered metal powder filled in the throughhole of the insulating substrate is formed, for example, by filling, in the throughhole, a metal paste composed mainly of copper, tungsten, molybdenum or the like and then conducting firing and wherein the two electroconductive layers are electrically connected with each other at least partially by the sintered metal powder. The submount according to the present invention has a low electric resistance and high reliability and can be made in a small size. Therefore, it can be suitably used as a novel submount for semiconductor laser element, which promises electrical conduction between a semiconductor laser element and a heat sink.