We fabricated and analyzed the chemical states of carbon-doped (5.2-13.2 at.%) Ge2Sb2Te5 thin films on Si substrates using high-resolution, X-ray photoelectron spectroscopy with synchrotron radiation. Thin films were completely amorphous and their phase-change temperature was 150 degrees C higher than for undoped GST. As the carbon doping concentration increased, new chemical states of Ge 3d with 29.9 eV and C Is with 283.7 eV core-levels were observed. The doped carbon was bonded only with Ge in GST and doping was saturated at 8.7 at.%. (C) 2014 Elsevier B.V. All rights reserved.