A theoretical model for the I-V characteristics of ion-implanted metal semiconductor field-effect transistors (MESFET’s) has been developed. A new formula for effective drift saturation velocity for electrons, and a Gaussian approximation for the inverse of reduced distances in the channel have eased the process of formulation. Theoretical formulas for early saturation of drain current and transconductance obtained in the framework of the Lehovec-Zuleeg procedure, are quite simple and accurate. When calculated results from the present model are compared with available experiments, an encouraging correspondence between the two is observed. When used to study the appropriateness of the velocity overshoot and the softening of pinchoff voltage, it suggests that both of these phenomena are real in shortchannel MESFET’s, and these need to be carefully accounted for in a realistic model. The model is equally applicable also to ion-implanted JFET’s.