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Micromachined microsieves fabricated entirely by dry etch processes with pore diameters ranging from 3 to 5 μm are reported. Two microsieve architectures are explored: 2.1 and 5.3 μm thin dielectric layer membranes supported by high aspect ratio rib features (10:1), and 50 μm thick silicon membranes from silicon-on-insulator wafers with no supporting ribs and high aspect ratio pore features (16:1). The flow throughput of each design is evaluated experimentally and theoretically, and the expected relative robustness is assessed and compared to typical microsieve structures reported in the literature. The experimental and theoretical work suggests that both structures have the potential for higher robustness than the typical micromachined microsieve architectures, with reduced but still reasonable flow throughputs in the range of 105 to 106 L/m2-hr-bar, depending on the microsieve porosity. Both microsieve architectures are shown to block monodisperse polymer beads 3 μm in diameter.