Differences between static and dynamic behavior of microwave transistors have been studied through different models. Behavioral models are very accurate for prediction of this phenomena without the necessity of electrical equivalent circuits. From other side, device level models based on semi-empirical equations can also model this phenomena by using non linear equivalent circuits but without the necessity of the knowledge of the physical parameters of the transistor. In this paper we will show the impact of the electrical mobility parameter in the prediction of the difference between static and dynamic behavior of microwave devices, establishing a link between this parameter and electrical equivalent circuits. Modeling and characterization of mobility for different transistors will be presented.