The real-time knowledge of the junction temperature of power devices is an essential asset to improve the power density of modern power converters. In fact, temperature is the main stressor in term of device reliability, and its accurate measurement enables dynamic derating and overload without any lifetime penalties. On-state resistance is a renown temperaturesensitive electric parameters for MOSFETs, which can provide reliable information, provided that an accurate characterization procedure is undertaken, for each particular device used. In this paper, we propose four possible ways to improve the accuracy and speed of this characterization procedure, especially when done in an in-circuit setup (as opposed to a laboratory one). These improvements pertain to: consideration of self heating also for short-time pulses, compensation of the nonidealities of the conditioning circuits, changes in the cooling system to reduce the duration of the procedure while improving the accuracy of the reference temperature sensor, adoption of simplified models for the fitting of the experimental data. The proposed solutions are evaluated using a custom active gate driver; final design guidelines for the improvement of the procedure are eventually presented, demonstrating the possibility to simplify the characterization procedure with respect to the state of the art, still retaining a high accuracy.