A critical factor in the design of high-performance, pulsed W-band IMPATT diodes is the accurate estimation of the transient intra-pulse junction temperature. For this reason, a simple physics-based model was developed to calculate the junction-temperature profile of IMPATTS operated with short, low-duty-factor pulses. The efficiency of the Tj profile as the model is called is demonstrated by considering a typical 5-W, W band, silicon DDR IMPATT diode.