An out-of-plane electrostatic comb actuator with in situ capacitive position sensing is presented. Asymmetrical vertical combs are used as the comb drives and in differential out-of-plane position sensing capacitors. A spring which can realize out-of-plane translational displacement of high-aspect-ratio structures was designed and analyzed both analytically and numerically. A robust silicon-on-insulator (SOI) process was proposed and verified to successfully fabricate the actuator with asymmetrical combs. The in situ capacitive position sensing capability was realized by the integrated out-of-plane sensing capacitors, and calibrated with the gravity as an acceleration reference. Treated as an accelerometer, the scale factor and nonlinearity of the actuator are evaluated to be and 0.03%, respectively, with the input range of . The tested static out-of-plane displacement ranges from to 1.39 μm when the actuator is placed horizontally, and to 1.25 μm when placed vertically, both with the supply voltage of 12 volts.