It is reported firstly that the plasma extraction transit time (PETT) oscillations occur under short circuit condition of high-power IGBT modules. First, a test platform with high-bandwidth test equipment is constructed to evaluate PETT oscillations under different short-circuit conditions, and the oscillation mechanism is characterized based on the carrier and electric field distribution inside the drift region during the short circuit turn-off process. Moreover, the effects of bus voltage, gate voltage (short current), junction temperature and gate resistance on PETT oscillations under short circuit conditions are analyzed based on experimental results. Finally, a method with package layout optimization to suppress PETT oscillations is proposed and the effectiveness of proposed method is verified by experiment.