A method for across-wafer critical dimension uniformity performance monitoring in the manufacture of semiconductor devices employs a number of optical endpoint detectors at sites at the wafer face which are spaced across the wafer face. Each optical endpoint detector is able to directly measure the end point of the process step at its site. One of these optical endpoint detectors is used to control the process, and when the endpoint has been reached for this site the process completion time is predicted and this completion time is used to control the processing equipment. For example, if the process step being monitored is the development of photoresist, then the developing operation is ended based upon this calculated completion time derived from the detected endpoint for the control site. The other sites are used to monitor across-wafer performance. The output of each of these other optical detectors is used to determine the endpoint for each monitor site, and these endpoints are compared with the control endpoint to determine across-wafer critical dimension performance and conformance to specification. The wafers can thus be flagged if out-of-limit, and need not be processed through subsequent steps.