The oxidation of InAs(1 1 1) surfaces has been studied by photoelectron spectroscopy. Both the InAs(1 1 1)A and the InAs(1 1 1)B surfaces are studied and it. is found that the initial oxidation follows different paths for the two surfaces. At low oxygen exposures of the A face the Fermi level structure, which is due to the electron accumulation layer, increases in intensity. On the B-side the intensity of the lone pair surface state decreases with increasing oxygen exposure. For larger exposures significant changes can be observed in the line shape of the In 4d and the As 3d core levels. (C) 2003 Elsevier Science B.V. All rights reserved.