Figures 1 (a), (b) and (c) show SEM images of 21 μm thick SU-8 pillars on silicon developed after PBW. These data demonstrate a capability of PBW to fabricate vertical pillars with a height of 21.0 μm and a width of as small as 1.1 μm with a high aspect ratio of 20, with a uniformity over 700 μm squared area. An optical microscope image in Figure 2 shows a part of a DEP device, where the high-aspect-ratio SU-8 pillars with a 12 μm pitch were formed in the gap between the two surface electrodes. Our preliminary investigation shows that Escherichia coli can be trapped at pillar structures under AC bias (3 volts, 100 kHz) of the two electrodes. The trapping behavior of DEP device with different structures and sizes will be examined.