The high speed photoresponse of a GaAs-MESFET has been demonstrated using a light pulse of about 100 ps duration with a 2 GHz repetition rate generated by a GaAlAs-DH laser diode. The measured current pulse heights through the gate and through the drain as a function of the gate bias voltage confirmed a theory that the photoresponse in MESFETs is caused by the sweepout effect of photogenerated carriers in the depletion layer extending from the gate to the drain, just as in photodiodes with subsequent ordinal FET amplification.