To reduce surface damage and achieve vertical profiles during selective etching of polysilicon, uniformity of the polysilicon across the wafer after the bulk etch step must be ensured. The bulk polysilicon gate etch process on a single-wafer plasma reactor was analyzed using response surface methodology to create models to be used in model-based process control. In situ etch rate data at the wafer center was collected using a single-wavelength ellipsometer. Off-line etch rate measurements at sites across the wafer were also made. The etch rate at each site was modeled as a function of the process factors and the ellipsometer response. By modeling each site as an explicit function of the ellipsometer response the proposed modeling approach allows the inference of process uniformity using the in situ sensor data only. As a result, the site models can be updated on-line to reflect the current performance of the process for run-to-run model-based process control. The updated models can be used for process optimization for evaluating the process settings (targets-to-settings) prior to running each wafer. In this paper the initial models were optimized to achieve a target etch rate while maintaining a uniform thickness of polysilicon after the bulk etch step (each site within 150 angstrom of the stopping thickness at the wafer center).