It is important to control the microstructure and surface of films to use them in gas sensors. Chemical mechanical polishing (CMP) processing is one of the most useful methods for improving the surface roughness of films. The effects of CMP on the surface morphology Of WO3 thin films prepared by the rf sputtering system were investigated in this article. The removal rate of the films increased, and the rms surface roughness decreased with the addition of an oxidizer to the tungsten slurry. Within-wafer nominiformity was improved to below 5% when oxidizers of 5.0 and 2.5 vol %, respectively, were added to the tungsten slurry. The optimized oxidizer concentration, reflected by both the rms roughness values and a hillock-free surface with the good uniformity, was 5.0 vol % as shown with atomic force microscopy analysis of thin film topographies. Our CMP results will be a useful reference for advanced technology of thin films for gas sensor applications in the near future. (c) 2005 American Vacuum Society.