A differential capacitive three-axis silicon-on-insulator (SOI) accelerometer using vertical comb electrodes fabricated by using surface-micromachining technique has been developed. The accelerometer structures consist of only the device layer of a SOI wafer without lower or upper electrodes. The vertical comb electrodes of this device have structures different from conventional vertical comb electrodes. The bottom faces of both movable and fixed electrodes are in the same plane at their initial positions but their heights are different. Three-axis acceleration can be sensed with differential capacitance detection by using only these vertical comb electrodes. The device structures were successfully fabricated using self-alignment and Deep-RIE processes. As an initial result, the capacitance changes against three-axis acceleration were observed and the device sensitivities to three-axis accelerations were measured. The capacitance sensitivities of X, Y and Z-axis were 1.01, 0.898 and 0.989 fF/G, respectively. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.