Abstract: A novel IGBT 3-D thermal model is implemented.The thermal distribution is simulated and analyzed by using the Finite Element Method-based analytical software ANSYS.Simulation results show that thermal coupling aggravate the self-heating of the device,it is becoming to select 10μm distance between cells,Temperature dependent thermal conductivity of Si was considered during simulation,the results indicate the peak temperature rise 4.8K in the same power（P = 1W）.When the die attach exists the void,the temperature distribution of IGBT is brought more changes,the surface temperature increase 24.9K in contrast with no void of the die attach.