The DC and RF characteristics of metal-semiconductor field-effect-transistors (MESFETs) on conventional CMOS silicon-on-insulator (SOI) substrates are compared to nominally identical devices on high-resistivity, trap-rich SOI substrates. While the DC transfer characteristics are statistically identical on either substrate, the maximum available gain at GHz frequencies is enhanced by similar to 2 dB when using the trap-rich substrates, with maximum operating frequencies, f(max), that are approximately 5-10% higher. The increased f(max) is explained by the reduced substrate conduction at GHz frequencies using a lumped-element, small-signal model.