The effect of power modulation on radical concentration and uniformity in a single-wafer plasma reactor was investigated with a radical transport, and and reaction model. Plasma etching of silicon using tetrafluoromethane under relatively high pressure (similar to 1 torr) high frequency (13.56 MHz) conditions was taken as an example system. Gas velocity, temperature, and radical concentration profiles were obtained numerically, by a finite element method. When compared to a continuous wave plasma, power modulation can alter the relative concentration of radicals and in turn the etch rate and uniformity as well as selectivity and anisotropy. Uniformity is improved by power modulation except at high flow rates which, however, result in poor, utilization of the feedstock gas.