Effects of Ge2Sb2Te5 and GeTe oxidation on their phase-change properties were studied by optical measurements and Parallel Angle Resolved X-ray Photoelectron Spectroscopy (PARXPS). The influence of oxygen on the active material was depicted in order to explain variations of the phase-change properties. The surface analysis evidenced a two-steps oxidation involving the formation of germanium and antimony oxides then tellurium oxide. A smooth surface sputtering allowed physically distinguishing the different oxides on GeTe sample overlayer and gave information about oxidation mechanisms. A significant drift of crystallization temperatures and activation energies were observed after 12 months air exposure time that points out the influence of the phase-change materials oxidation on their active properties. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.027204jes] All rights reserved.