The purpose of this study is to investigate the planarization behavior of high selective ceria slurry in terms of topography and pattern density variation. Planarization experiments have been performed using ceria slurry with various initial step heights and surrounding pattern density on active trench and shallow trench isolation. The threshold step height was measured in various layouts which showed different pattern density ranges, and the pattern density effect on the threshold step height has been discussed. The planarization capability of high selective slurry and the removal rate of the high density plasma oxide are strongly dependent on the whole chip topography rather than on the micropattern density.