It is shown that a nonquasi-static analysis must be used to describe the transient current and voltage waveforms of the IGBT (insulated-gate bipolar transistor). The nonquasi-static analysis is necessary because the transports of electrons and holes are coupled for the low-gain, high-level injection conditions, and because the quasi-neutral base width changes faster than the base transit speed for typical load circuit conditions. To verify that both of these nonquasi-static effects must be included, the predictions of the quasi-static and nonquasi-static models are compared with measured current and voltage switching waveforms. The comparisons are performed for different load circuit conditions and for different device base lifetimes. >