4H-SiC metal-semiconductor field effect transistors (MESFETs)  were characterized at 25; 100; 150; 200; and 250Â°C and two-dimensional electro-thermal simulations  were performed to examine the effects of elevated device operating temperature and self-heating on DC and RF performance of the MESFETs. The gate and drain characteristics (Id-Vg & Id-Vd) were measured at room and elevated temperatures. The pinch-off voltage increased with temperature and drain voltage. The shift of the pinch-off voltage was more prominent at low temperatures (2 V from 25 to 100 Â°C) than at high temperatures (negligible shift above 150 V). No short channel effects could be seen in drain characteristics due to the self-heating effects. The measured knee voltage and saturation current differed to some extent from the simulated values; which could be caused by the surface and the substrate traps that were not included in the simulations due to the difficulty to describe the temperature dependence of the trap behaviours. The current gain and power gain were measured as a function of frequency. Decrease of fT and fmax with increase of temperature was observed for both measurements and simulations. Higher fT and fmax were obtained from simulations than from the measurements. Traps and parasitics are believed to be the cause for the differences. A strong influence of contact resistance was seen on fT and fmax in the HF simulations.