The design, fabrication, and testing of a micromachined tangential flow filtration device is presented. The filter design incorporates three stages of size-based filtration on a 1cm × 1 cm silicon substrate, which provides a band-pass filtration scheme and flexibility for flow control in filtering and unclogging operations at different filtration stages. 3-D flow simulations suggest means to determine the optimal flow control conditions. Fluorescent microscopy results show the proof of concepts of the filter design, with particle retentant ratio over 95% in all three filtration stages.