Oxidation of sintered aluminum nitride at low temperatures (20°–200°C) was studied using transmission electron microscopy (TEM). Particles of α‐Al2O3, about 20–30 Å in size, were found to form within minutes on freshly cleaned surfaces of AlN at room temperature. The oxide was found to grow nearly epitaxially on AlN when the {0001}AlNplanes were exposed to the surface. Limited nonepitaxial oxidation was also observed when the basal planes were inclined to the TEM foil surface. After 10 h in air at 75°C, the particles coarsened to about 50 Å, while after 150 h at 200°C, an oxide film, about 500 Å thick, was observed o