Nanopotentiometry is a scanning probe microscopy (SPM) technique providing insight in the actual working behavior of semiconductor devices under operation. In nanopotentiometry, a conductive SPM tip is used as a voltage probe in order to measure the distribution of the electrical potential on the cross section of an operating device. The information thus provided, is complementary to carrier profiling and is a method for the calibration of device simulations, The suitability of alternative SPM techniques for studying ultrashallow devices under operation is examined. Measurements have been carried out in deep submicron complementary metal-oxide-semiconductor devices. The impact of the changes in the doping profile on the potential distributions has been explored using simulations and experimental results. Due to further improvements in sample; preparation and measurement methodology, the response of the devices to variable bias conditions could be studied in more derail. The formation of the conductive channel underneath the gate was investigated and compared to device simulations.