Transconductance frequency dispersion measurements were performed on fully implanted MESFETs made on bulk semi-insulating 4H-SiC to observe bulk, as well as surface, traps in the channel region. A 30% reduction in the transconductance was observed by increasing the frequencies from 0.1 Hz to 10 MHz. Five traps were recorded in this study. Bulk traps observed at 0.52 and 0.65 eV in the gated channel region, which were also seen in the capacitance-DLTS study, are believed to be due to the nitrogen implant-defect complex and vanadium deep donor dopant, respectively. Surface traps of the ungated channel region between the source and gate and gate and drain were observed at 0.18, 0.3 and 0.4 eV. The trap at 0.4 eV has shown an upward transconductance dispersion behavior with increasing frequency, whereas all the remaining four traps have shown a downward frequency dispersion behavior. The origins of the surface traps are not known at this time. (C) 2003 Elsevier Ltd. All rights reserved.