The freewheeling diode in power electronic converters may generate a voltage peak on the load during the reverse recovery process, and the peak voltage becomes larger when the forward conduction time is smaller, which very likely induces the over-voltage failure of the power devices. To effectively guide the reliability design of power electronic devices, the switching transition mechanism of the PIN freewheeling diode is discussed thoroughly based on semiconductor physics and the essential structure of power diodes. The law of reverse recovery voltage peak variation with switching transition time is deduced by methods of stored charge analysis, which shows that the peak voltage is larger for shorter conduction time and decreases abruptly as the transient conduction time increases. Experiments are carried out using the two-level half-bridge inverter unit with insulated-gate bipolar transistors and PIN diodes. Results show that the reverse recovery voltage peak decreases with the increase of the transition time, following an exponential rule, and tends to be constant after the freewheeling current becomes stable and finally approaches a steady state as the steady forward conduction current vanishes, thus proving the correctness of the presented analysis. This paper shows the theoretical and application values in the optimization of the reverse recovery mechanism of power diodes and the reliability improvement of power converters.