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Close-packed arrays of microplasma jets, propagating into atmospheric air with uniform plume length and luminosity, have been generated in cylindrical microchannels and characterized. Arrays as large as 8 × 8 with a packing density of ~160 cm-2 have been demonstrated to date. Fabricated in a molded flexible polymer that is transparent deep into the ultraviolet (λ ≳ 250 nm), microchannel devices 350 μm in diameter generate plasma in He feedstock gas with a backing pressure of 760-900 Torr and flow rates up to 4.6 standard liters per minute. Chemical kinetics of the He (21,3S) and He2 (a3Σu+) excited species interacting with laboratory air has been examined by optical emission spectroscopy. The maximum jet length for a 5 × 5 array is 3.8 ± 0.2 mm when the He backing pressure is 840 ± 20 Torr. Relative to previous jet array designs, this technology increases the jet packing density by more than an order of magnitude and yet jet-jet interactions are not observed.