From the analyses of MESFETs with gate finger width of 50 mum, an extrinsic input capacitance was found to deteriorate dramatically their cut-off frequency. To examine the influence of the capacitance generated by connection pad and line of FET, we fabricated different gate finger width MESFETs. With increasing gate finger width, improvement of cut-off frequency was observed. Cut-off frequency of 10.0 GHz was obtained at gate finger width of 1.0mm. RF output power performance was measured under on-wafer. An output power of 2.1W and output power density of 2.5 W/mm was obtained.