A microfabricated pillar array separation column which has a comparable theoretical plate number to the conventional packed column was fabricated on a silicon chip. The column has a folded separation microchannel with compensated narrow curve structures which have inner and outer paths of the same length. This geometry minimizes the turn-induced band broadening and achieves high separation efficiency. The liquid chromatography (LC) microchip was fabricated on the 20 mm x 20 mm silicon chip using a column of 110 mm in length. The theoretical plate number is approximately 8000 (typical packed column: 5000-18000) and the plate heights are 10.4 ?m (typical packed column: 14-20 μm). These results show that the microfabricated LC microchip is suitable for practical uses.