A study of ion-implanted MESFET performance as a function of the implantation energy and fluency, and including the effects of deep-level trapping-state concentrations in the substrate, has been conducted. Carrier concentrations as a function of depth are determined through the use of LSS theory and a profiling model. An analytic device model, which computes both dc and RF characteristics, is then employed to predict MESFET performances. The study includes the effects of depth-dependent transport properties and has indicated a number of design rules for the fabrication of optimized ion-implanted devices.