Abstract: In plasma processing, a bias voltage is provided from a power supply through a DC blocking capacitor to a platform on which a substrate to be treated is supported within a plasma reactor. The periodic bias voltage applied to the DC blocking capacitor has a waveform comprised of a voltage pulse peak followed by a ramp down of voltage from a first level lower than the pulse peak to a second lower level, the period of the bias waveform and the ramp down of voltage in each cycle selected to compensate for and substantially cancel the effect of ion accumulation on the substrate so as to maintain a substantially constant DC self-bias voltage on the substrate between the voltage pulse peaks. The waveform may include a single voltage pulse peak followed by a ramp down in voltage during each cycle of the bias voltage such that the ion energy distribution function at the substrate has a single narrow peak centered at a selected ion energy.