The thermal oxidation of the beta-Si3N4(0001)-8 x 8 surface has been carried out. The spectroscopic characterization has been performed by high resolution core-level and by angle-resolved photoemission spectroscopy. Our findings demonstrate that the surface shows a low but clear reactivity with oxygen. The known resonance ascribed to the 8 x 8 reconstruction results strongly affected by the oxygen dosing, demonstrating the involvement of the topmost nitride atoms. (C) 2015 Elsevier B.V. All rights reserved.