Numerous CAD models are proposed today in the literature for GaN HEMT devices. They all have their place in circuit design. It just depends on which type of criteria and properties that the models should be able to simulate. Indeed, a physic-based model is very useful in the design phase of the device design, but unfortunately you will not have access to the structure of the transistor. Moreover, the use of this model in harmonic balance simulation will be limited due to the time consuming and non-convergence. Other models are mainly based on empirical or equivalent circuit approach. In the last ten years, a new type of models has appeared. Based on the definition of the surface potential [1][2], they represent a good alternative to other modelling approach especially in terms of scalability and model performance [3] for applications where accurate distortion modeling is of paramount importance.