Abstract: A chemical mechanical polishing system for processing semiconductor wafers has a polishing arm and carrier assembly that press the topside surface of a semiconductor wafer against a motor driven, rotating polishing pad. Improved uniformity of material removal, as well as improved stability of material removal rate, is achieved through the use of a controller that applies a variable wafer backside pressure to the wafers being polished. More specifically, a control subsystem maintains a wafer count, corresponding to how many wafers have been polished by the polishing pad. The control subsystem regulates the backside pressure applied to each wafer in accordance with a predetermined function such that the backside pressure increases monotonically as the wafer count increases. In the preferred embodiment, the control system regulates the backside pressure in accordance with a linear function of the form: Backside Pressure=A+(B.times.Wafer Count).