Abstract: In this paper a new method for calculating the noise parameters of MESFET is presented. Using this method, noise parameters can be calculated not only from structure parameters or S parameters of MESFET separately, but also from the structurc parameters and S parameters simultaneously. This method possesses higher precision than those methods in common use. In this method noise parameters are calculated by using the rigorous network theory and lead inductances are included in the equivalent circuit of MESFET, so this method can be used up to a higher frequency range than Fukui's. Program MESNOC realizes these ideas. It is very useful for research and development of new device as only the nodes of the equivalent circuit and the values of the elements are required when unning MESNOC. The values of minimum noise figure calculated by using MESNOC agree with the values measured.