We have developed a simulation model based on the solution of the Boltzmann transport equation (BTE) for modeling n-channel silicon-on-insulator (SOI) metal-semiconductor field-effect transistor (MESFETs) using the ensemble Monte Carlo device simulation technique. All relevant scattering mechanisms for the silicon material system have been included in the model. In addition to phonon scattering, to properly describe the operation of the SOI MESFET devices, in our theoretical model we have also included surface or interface-roughness scattering. Following Fischetti and Laux[J. Appl. Phys. 89, 1205 (2001)] we first model interface roughness as a real space scattering event, separated into specular and diffusive (isotropic) type of reflection from an ideal atomically flat interface. This model gives rise to low-field silicon electron mobility values in agreement with available experimental data. To further verify our mobility results, we also treat interface roughness as a boundary condition based on the Boltzmann-Fuch method. To examine the performance improvement of this device structure, in contrast to some previous studies, here we have simulated analogous SOI MESFET and SOI MOSFET devices. The results of these investigations suggest that the mobility of the SOI MOSFET device follows the experimental values and the mobility of the SOI MESFET is three to five times higher than that of the SOI MOSFET in the subthreshold and the on-state regime. These high mobility values suggest that this device structure is a promising candidate for low-power high-frequency applications.