Continuing progress in the microelectronics world has enabled the development of faster, denser and more complicated circuits. These technological advancements have rendered the internal probing of these circuits both difficult and necessary for performance evaluation and failure analysis. Existing probing techniques do not satisfy the combined requirements of high spatial resolution, high temporal resolution, non-invasiveness, high sensitivity, absolute voltage measurement and simplicity. An alternative internal probing technique based on the electro tatic force microscope (EFM) is investigated in this research. The localized electrostatic interaction between a small conducting probe and the test point is used for non-contact measurement of signals on microelectronic structures. A heterodyne technique is employed to measure periodic high frequency digital and sinusoidal signals using the EFM instrument. Vector voltage measurements are performed on the internal nodes of a commercial MMIC amplifier and a MHMIC phase shifter. A nulling technique is used for absolute voltage measurements of sinusoidal signals up to 2GHz. A pulse sampling heterodyne technique is used for the measurement of arbitrary periodic digital patterns. Measurements of 1Gb/s digital patterns are demonstrated on the internal nodes of a BiCMOS circuit.