A physics-based model of insulated gate bipolar transistor (IGBT) with all free-carrier injection conditions in a base region is presented, from which the ambipolar transport equations (ATEs) in high-level injection and low-level injection are deduced separately. Moreover, the boundary conditions of ATE are determined. In a more compact solution a Fourier-series solution for the ATE is used in this paper. Simulation and experimental results given by manufacturers are presented and compared with each other to validate the modeling approach. Physics-based IGBT model is used which is proved accurate.