Nowadays, even though ESD protection diodes are clearly the most used protection devices in I/O cells their behavior is a major problem during a very fast transient. In fact the forward and reverse recovery effects lead respectively to a high over voltage during their triggering and a sustained voltage during the turn-off. Those phenomena depend on the time needed by minority carriers to flow or evacuate the neutral region (the well). This time, which is the transit time of the diode, is also a key parameter of the diode transient behavior. In this presentation a simple extraction method is described in order to extract the transit time of an ESD protection diode. Then, the impact of the junction shape on the transit time will be demonstrated.