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A new two-dimensional (2-D) analytical model for the threshold voltage of a fully depleted short-channel Si-MESFETs fabricated on the silicon-on-insulator (SOI) has been presented in this paper. The 2-D potential distribution functions in the active layer of the device is approximated as a parabolic function and the 2-D Poisson's equation has been solved with suitable boundary conditions to obtain the bottom potential at the Si/oxide layer interface. The calculations have been carried out for both uniform and nonuniform doping profiles in two dimensions. The minimum bottom potential is used to monitor the drain-induced barrier lowering effect and consequently an analytical expression for the threshold voltage of the device has been derived. The numerical results for the bottom potential and threshold voltage considering a wide range of device parameters have also been presented. The model has been compared with the simulated results obtained by using the ATLAS Device Simulation Software to show the validity of the proposed model. For uniform doping profile, the numerical results have also been compared with the reported data in the literature and a good agreement is observed among the three. The proposed model is simple and easy to understand the behavior of the fully depleted short-channel SOI-MESFETs as compared to the other models reported in the literature.