4H-SiC metal-semiconductor field effect transistors (MESFETs) [1] were characterized at 25, 100, 150, 200, and 250 degreesC and two-dimensional electro-thermal simulations [2] 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 (I-d-V-g & I-d-V-d) were measured at room and elevated temperatures. The threshold voltage decreased with temperature and drain voltage. The shift of the threshold voltage was more prominent at low temperatures (2 V from 25 to 100 degreesC) than at high temperatures (negligible shift above 150 degreesC). No short channel effects could be seen in drain characteristics due to the self-heating effects. The measured drain saturation current decreases with increase temperature. At lower gate and drain voltages the measured drain current at room temperature is smaller than the drain current at elevated temperatures. The threshold voltage shift and the lower drain current at room temperature are believed to be caused by the substrate traps, which induce extra charges at the channel-buffer interface acting as a backside gate. The current gain and power gain were measured as a function of frequency. Decrease of f(T) and f(max) with increase of temperature was observed for both measurements and simulations. Higher fT and f(max) 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 f(T) and f(max) in the HF simulations.