This paper describes the development and implementation of an analytical thermal model for fast and accurate thermal simulations of power device modules. A Fourier-based solution is used to solve the heat equation in two dimensions. The solution can describe the variation of temperature through the structure versus time. The thermal model is extremely fast to simulate compared to finite-element (FEM) approaches. The new model has been implemented in MATLAB/Simulink. The model has been validated against FEM simulations and the difference between the two models has been illustrated. The required aspects of heat diffusion are captured successfully by the Fourier-based model.