AbstractThis article presents a signal flow graph representation for a microwave MESFET equivalent circuit. The model has been found to provide accurate fits to NE71000 MESFET chip scattering parameters; typical results are shown. Four symbolic transfer functions are presented which allow device scattering parameters to be computed. The symbolic transfer functions can be differentiated in order to determine component or device behavior sensitivities; sample formula are presented. The principle advantage of the symbolic transfer function approach is that when used as the function evaluation engine in a numerical optimization scheme computational overhead is small. In addition, having analytical derivatives available allows for rapid gradient and sensitivity evaluations that are not prone to numerical approximation inaccuracies.