This letter presents a technique for performing localized noncontact measurements of high frequency signals on integrated circuits using a scanned force microscope. The technique extracts the amplitude and phase of the signal voltage at a point on the circuit by nulling the electrostatic force interaction between a small driven probe and the test point. A heterodyne approach is used to enable the measurement of high frequency signals, including frequencies which are much greater than the mechanical resonance of the probe mechanism. Accurate measurements can be performed without complex calibration requirements and are not sensitive to dc offset effects.