Results are presented from a design of experiments targeted towards extending the use of ion-implanted MESFETs to higher frequencies. The implant schedule is optimized to achieve a shallow, abrupt profile while maintaining high peak carrier concentration. Minimizing the source-drain spacing improves the high frequency performance. The resulting d-mode and e-mode devices both have f t over 120 GHz and f max over 160 GHz, making the device an excellent candidate for low-cost, high-performance wireless and fiber channel applications.