This article is concerned with the effect optical intensity has on the frequency response, gain, and bandwidth of the GaAs MESFET when used as an optical detector. Measurements show that the photoresponse gain can be increased by 10 dB as the optical intensity is lowered, while the bandwidth of the MESFET can be increased by an order of magnitude with an increase in optical power. © 1993 John Wiley & sons, Inc.