Previously we reported a method to measure the transient temperature of transistor junctions under pulse operation. The method was such that the transient temperature of the junction was measured through Icbo pulse current, but to know a whole temperature decay during the recess time of power pulses,  Icbo pulses were shifted manually point by point in their phase with use of Delay Circuit.
It leads to several diffculties such as in setting the phase shifts of Icbo pulses, in reading the junction temperatures correctly and also it takes a lot of time to complete the whole decay of the temperature of the transistor junction. This means we could not expect good accuracies.
In this time, the temperature behavior during the recess time of the power pulses can be measured continuously and easily to be observed on an oscilloscope. The new method can take those diffculties away and gives good accuracies. At the same time, it becomes possible to observe both temperature rise of the junction after switch-in and temperature fall after switch-off of power pulses. Also it could easily obtain thermal time constants, the maximum and minimum temperatures of the transistor under pulse operation and the limit of thermal runaway conditions.