Semiconductor manufacturing is challenged by strategy development for ensuring the yield of defect-free products. In this paper, an on-line performance assessment strategy is proposed to evaluate the EWMA-based run-to-run (RtR) controllers in a discrete microelectronics fabrication. Expressions of minimum variance performance (MVP) and best achievable performance (BAP) are derived in a rigorous way. Technologies such as close loop identification and numerical optimization are employed in order to carry out on-line monitoring. Case studies of the chemical mechanical polishing (CMP) unit operation show the efficacy and the attractiveness the strategy.