To consider the nonlinear and 2-D characteristics of the carriers in the draft region of a planar-gate insulated-gate bipolar transistor, which are not properly modeled in the existing physics-based IGBT models, a 2-D ambipolar diffusion equation model is proposed and solved using the finite-element method. Moreover, a numerically iterative procedure is introduced to simply and efficiently solve the 2-D nonlinear finite-element equations. The numerical results of the transient performances obtained using the proposed model and solution methodology show a good agreement with those of the experiment ones, showing the high accuracy and feasibility of the proposed model and method.