Chemical mechanical polishing (CMP) is considered to be the enabling technology for meeting the planarization requirements in <0.35 mu m feature sized multilevel semiconductor device fabrication. CMP of tungsten is done in order to planarize and remove excess tungsten in the process to form inter-level contacts. Considerable importance is given to the role played by the passive oxide film formation on the surface during tungsten CMP. In this study, x-ray photoelectron spectroscopy (ICPS) is used to understand the oxide growth mechanism in tungsten. Tungsten wafers are polarized to different anodic potentials in static pH 4 solutions of KIO3 and H2O2, two commonly used oxidizers in CMP. XPS measurements are employed to probe the chemical and stoichiometric changes in the surface oxide films treated under these conditions. These results are then compared with the electrochemical polarization results.