We investigated the chemical mechanical planarization (CMP) mechanism of nitrogen-doped polycrystalline Ge2Sb2Te5 (pc-GST) using nitric acid slurry without or with 1.0 wt % hydrogen peroxide (H2O2). Without H2O2, the pc-GST film surface undergoes selective corrosion of Ge and Sb, resulting in pitting corrosion. Otherwise, with H2O2, the pc-GST film surface produces a Ge, Sb, Te oxide layer, thereby introducing a cyclic polishing process such as chemical oxidation, chemical and mechanical polishing, and sequential chemical oxidation. As a result, the polishing rate increased up to similar to 1000 angstrom/min and the surface roughness decreased to 0.858 nm. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3571529] All rights reserved.