Reactive-plasma etching is conventionally carried out using one power supply to both generate the glow discharge and to control the flux and energy of ion bombardment on the substrate. A three-electrode, or triode, configuration is described in which these two functions are controlled quasi-independently; results obtained with this arrangement are described. These results are somewhat similar to those obtained with a diode RIE system, except that control of the substrate voltage allows another degree of freedom over etch rates, etch selectivity, and wall profiles.