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The drain-induced barrier lowering (DIBL) effect and its dependence on the channel doping concentration in 4H-SiC metal semiconductor field effect transistors (MESFETs) have been studied using the physical drift and diffusion model. Our simulation results showed that the high drain voltage typically applied in 4H-SiC power MESFETs could drastically increase the threshold voltage when the ratio of the gate length to channel thickness (Lg/a) is less than 3. Larger channel doping concentration has also been found to enhance the DIBL effect, particularly at small Lg/a ratio. In order to minimize the DIBL effect, the ratio of Lg/a should be kept greater than 3 for practical 4H-SiC MESFETs, especially when the channel doping is more than 5×1017 cm-3.