Arrays of Al/Al2O3/glass microplasma devices with microcavities having diamond or circular cross-sectional geometries and radiating (active) areas >20 cm2 have been operated sealed-off in Ne, Ar, and Ar/D2 gas mixtures. Microcavities are fabricated in only one of the two electrodes, and the thickness of the completed package is ∼ 170 μm (excluding the quartz output window). Excited by a sinusoidal 20 kHz voltage wave form, arrays with active areas of 4.5×3 cm2 exhibit ignition voltages as low as 110±5 V rms for Ne pressures of 400–700 Torr. Mixtures of 1% D2 in Ar at a total pressure of 300 Torr produce wavelength-integrated (λ ∼ 250–400 nm) intensities of ∼ 1 mW cm−2 over a 25 cm2 area. Optical micrographs show the operation of the microplasmas in two well-defined modes. For current densities below a threshold value ( ∼ 53 mA cm−2 for 250 μm dia. cavities and pNe = 400 Torr), diffuse uniform plasma is produced in each cavity but, with higher currents, a positive column having near-cylindrical geometry appears, as evidenced by the generation of intense emission localized in the region of weak electric field gradient near the axis of symmetry.