Electrical characteristics of high performance GaN modulation‐doped field‐effect transistors (MODFETs) grown by reactive molecular beam epitaxy method are studied experimentally both in dark and under white light illumination. The maximum measured drain‐source current is 626 mA/mm in dark and 695 mA/mm under illumination, which saturates at a relatively low drain‐source voltageVDS. The transconductance increases with decreasing gate length reaching a value of 210 mS/mm in dark and 222 mS/mm under illumination for devices with a gate length ofLG=1.5&mgr;m. Breakdown voltages of about 90 V have also been exhibited by devices with gate lengthLG=1.5 &mgr;m and drain‐gate distanceLDG=1 &mgr;m. To our knowledge, these are the best values obtained so far from GaN MODFETs which we attribute to the suppression of leakage currents and improved materials structure of the devices. ©1996 American Institute of Physics.