The corrosion of aluminum nitride (AIN) in aqueous solutions has been evaluated in situ, using an ammonium/ammonia ion-selective electrode. The corrosion behavior of AIN over a pH range of 5.5-12 indicates that the corrosion products that are formed act as a protective barrier layer in the pH regime where they have the lowest stability, An insoluble barrier layer is formed via the oxidation of the AM surface in air at a temperature of 750 degrees C for 10 min. This oxynitride layer, which is 200 Angstrom thick, prevents the corrosion of the AlN in a pH 9.5 aqueous solution; however, the thermal conductivity is reduced by 6.6%.