We fabricated a 0.5 mum gate MESFET with a combination of optical and electron-beam lithography technique. A cutoff frequency and a maximum oscillation frequency were 2.8GHz and 8.6GHz, respectively. And we measured the source resistance of MESFET and found that it was 76 Omega. This value was about 4 times higher than that of 22.6 Omega calculated by using TLM results, the specific contact resistance of rho (c)=2.2x10(-5) Omega .cm(2) and the sheet resistance of rho (sh)=657 Omega/square. This difference between measured 76 Omega and calculated 22.6 Omega was caused by the high value of rho (sh) under the contact, which could not be obtained from TLM measurements. Nickel ohmic contact reacts with SiC underneath and makes Ni-silicide which penetrates by 0.2 mum into the ni contact layer and reduces its thickness. This Ni-silicide formation increased rho (sh) under the contact by a factor of ten compared to that of the initial contact layer.