Void formation and compositional change in nitrogen doped Ge2Sb2Te5 (NGST) films during repeated phase transformations were examined. Stable reversible switching behavior between the crystalline and melt-quenched phase of NGST films containing 5% nitrogen was examined using laser irradiation on a nanosecond time scale. Transmission electron micrographs indicated that with repeated phase transformation, void formation and subsequent coalescing and movement to the top and bottom interfaces with SiO2 layers in NGST occurred in both amorphous and crystalline states. Moreover, void formation at the grain boundaries of crystalline NGST was clearly observed. Compositional change around voids also occurred, which was confirmed using energy dispersive spectroscopy. Void formation and compositional change during repeated reversible switching can cause serious issues related to the reliability of NGST materials during actual phase-change random access memory device operations. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3547702] All rights reserved.