Cerium dioxide (CeO2) is one of the most widely used materials for oxygen gas sensors. The surface roughness of CeO2 thin films must be improved because the electrical and sensing properties of CeO2 thin films are determined by these characteristics. The authors selected chemical mechanical polishing (CMP) processing for improving the surface roughness of CeO2 thin films. The authors examined the removal rate and surface roughness of spin coated CeO2 thin films with a change of CMP process parameters such as pressure (down force) and velocity (table speed). An optimized process condition, reflected by not only the surface roughness with a hillock-free surface but also an excellent removal rate with good uniformity, was obtained. The effects of the improved surface roughness on the sensing property of CeO2 thin films were also confirmed. The authors obtained improved sensitivity of CeO2 thin films for oxygen sensors after, the CMP process by the improved surface morphology. Therefore, the authors concluded that the sensing property of CeO2 thin film was strongly dependent on the surface roughness of CeO2 thin films by using a CMP process. (C) 2008 American Vacuum Society.