Abstract: The hydrodynamic model (HDM) is presented for the transient simulation of GaAs metal-semiconductor-field-effect-transistor(MESFET) which works at high electric fields and frequencies. The finite volume discretization scheme and operator split method used for solving the HDM equations are discussed. A two-dimensional MESFET device is numerically simulated by using the HDM. Some typical numerical results are presented, such as the I-V curves, distribution of electron density and temperature of the device, etc. The results show that while the gate biases are more negative, the Schottky depletion layer is thicker and the source-drain current flow is lower. In the region of high electric field, the electron temperature is much higher than the lattice temperature, and the so-called hot electrons