Abstract: Preferred embodiments of the invention provide semiconducting microcavity plasma devices. Preferred embodiments of the invention are microcavity plasma devices having at least two pn junctions, separated by a microcavity or microchannel and powered by alternate half-cycles of a time-varying voltage waveform. Alternate embodiments have a single pn junction. Microplasma is produced throughout the cavity between single or multiple pn junctions and a dielectric layer isolates the microplasma from the single or multiple pn junctions. Additional preferred embodiments are devices in which the spatial extent of the plasma itself or the n or p regions associated with a pn junction are altered by a third (control) electrode.