We developed a micromachining process for the fabrication of highly sensitive capacitor probes to be used for displacement measurement of an atomic force cantilever. The capacitive structure consists of two adjacent single-crystal silicon beams, one carrying a sharp tip for the force interaction, the other being the counter-electrode. The air gap of 1.5 pm separating the two electrodes is obtained by removal of the oxide in between by selective etching. The capacitance has a typical value of -0.2 pF. Forces acting on the tip induce a bending of the cantilever and change the caDacitance which can be detected by electronic circuits.