Characterization of a high selectivity polysilicon chemical mechanical polishing (CMP) is studied in this report. The process is developed for the fabrication of two-dimensional secondary ion mass spectrometry (2D SIMS) test chip, in which a silicon trench is filled with polysilicon and polished back in an effort to create a flat surface. In this application, the polysilicon surface roughness and the step height between polysilicon and c-Si substrate must be minimized. Atomic force microscopy shows that the CMP process reduces polysilicon surface roughness. The step height between polysilicon and c-Si substrate can be minimized by choosing the proper thickness for the polish-stop layer (e.g., silicon nitride) over the c-Si surface. We found that the step height between the polysilicon and the c-Si surface is relatively sensitive to thr opening of the trench, but not sensitive to slurry selectivity and total polishing time. We speculate that deformation of the polishing pad is critical for the trench recess. In addition, we discuss important issues of characterizing the trench recess. Using a histogram of height, the high and low modes of the distribution are sometimes used to identify the trench recess. We showed that this approach results in various offsets from the peak-to-valley height.