This paper deals with parameter extraction as well as modeling of small signal GaAs MESFET that works as a control device. MESFET is quite similar to JFET in construction and terminology. The difference is that instead of using a p-n junction for a gate, a schottky (metal - semiconductor) junction is used .MESFET are usually constructed in GaAs.It is a compound semiconductor which has high electron mobility, can operate practically up to 30ghz approximately, and has less noise figure than Si.Hence it is faster than silicon based JFETor MOSFET. Small signal modeling is a common method used to relate the electrical performance of the device to the material and physical parameter of the device. We extracted the parameters of small signal model device. Intrinsic parameter determined in here by a conventional analytical parameter transformation technique are described as function of extrinsic element. We are using here MATLAB coding for optimization and S-parameter, Z-parameter, Y-parameter for circuit computation. The model is used as a switch in control application.