This article presents a sampling electrostatic force microscopy technique for high frequency integrated circuit internal measurement that utilizes a pulse width modulation method. The electrostatic force microscope is a class of scanning probe microscopes that is capable of providing noninvasive measurements of the electrical signals inside operating integrated circuits with very high spatial resolution. With this technique, the internal circuit voltage is determined by sensing the local electrostatic force on a miniature probe cantilever that is closely positioned above the circuit test point. The ability to extract repetitive voltage wave forms using direct force measurement is typically limited by the mechanical response of the probe. To overcome the measurement bandwidth limitation of the electrostatic force microscope previous methods have employed a modulated high bandwidth sampling pulse approach. The temporal resolution of these pulse sampling methods is limited by the pulse width. This article presents a pulse width modulation method. The resolution of the pulse width modulation technique is not dependent on the pulse width, but rather on the modulation depth. This enhances measurement resolution several times more than previous methods. The current instrument has a voltage sensitivity of 10mV(rms)/Hz(1/2).