This paper presents case studies that examine low voltage, low current electrical characterization and analysis of data that could help identify root cause failure mechanisms for soft transistor failures, providing a review of Vt shifts and blocked LDD implants review. The case studies demonstrate the importance of getting the most information possible out of all aspects of the nanoprobe electrical characterization results for failing transistors. Technology computer aided design (TCAD) modeling of transistor defects will be a useful tool for the nanoprobe analyst to identify the subtle defects that can only be identified through careful electrical characterization in conjunction with process analysis and experiments by the manufacturing facility. However, modeling at the transistor level has its difficulties. The key will be to build a library of electrical signatures with corresponding defects as they are discovered.