Oxygen-free and amorphous Ge1Sb2Te4 thin film was obtained in an ultra-high vacuum and then annealed in Situ to the stable-phase temperature. High-resolution X-ray photoelectron spectroscopy using synchrotron radiation was performed on the film at the different annealing temperatures of 100, 130, 150, 180, and 250 degrees C. The Te 4d, Sb 4d, and Ge 3d shallow core levels as well as the valence-band spectra were acquired. In the shallow core-level spectra, we observed distinguishable changes in the Sb 4d and Ge 3d levels as the film phase changed. As the temperature increased, a higher binding-energy (BE) component appeared at the Sb 4d level, the intensity of the component increased, and the spin-orbit split feature was enhanced at the Ge 3d level. In the valence-band spectra, a slight increase was observed at 0-1, similar to 3, similar to 9, and similar to 12 eV BE, and a decrease, at similar to 1.5 and similar to 4.5 eV BE. The energy resolution employed in this study was about 150 meV. (C) 2009 Elsevier B.V. All rights reserved.