A surface-treatment method for AlN substrates to improve adhesion with thick-film conductors has been developed based on the interfacial reaction mechanism between 96% alumina and glasses. The surface-treated AlN substrates were prepared through a combination of oxidation and sol-gel processes. An oxidation atmosphere with high P-O2 and low P-H2O, which produced the densest Al2O3 layer on AlN, was selected as the oxidation conditions for the surface treatment. A SiO2 layer was deposited on the Al2O3 layer, using the dipping technique with a sol-gel solution. The surface-treated AlN substrates with adequate thicknesses of Al2O3 and SiO2 as the surface-treatment layers showed a good adhesion strength with conventional thick-film conductors. This is the same result as with the 96% alumina substrates, although the adhesion strength of the conductors with bare AlN substrates was poor. These results suggest that glasses in the thick-him conductors react with the surface-treated AlN substrates in the same way as they react with the 96% alumina substrates, and also that the surface-treatment layer consisting of Al2O3 and SiO2 on AlN substrates is effective because it provides good adhesion between such substrates and conventional thick-film conductors.