Abstract: A novel empirical large-signal capacitance model for 4H-SiC RF power MESFET is presented based on the operational principle of devices. The least squares method and genetic algorithm are used to optimize the parameter extraction,and MATLAB is used to realize it. Compared with the traditional algorithm, the initial value computing and optimizing of model parameters is more simple and accurate. The main extracted parameters are physical proposed, and other fitting parameters also have physical magnitude. The simulation result fits well with the testing data, which shows the present model has good accuracy.