A 2D analytical model for the potential profile in the semiconductor channel of two-dimensional (2D) Dirac-Source (DS) FETs is worked out and compared with a rigorous numerical solution of Poisson’s equation. This analytical solution holds validity in weak inversion and enables a precise assessment of the subthreshold swing (SS) under the constraint of ballistic transport. When the device is biased in strong inversion, instead, a semi-empirical approach is worked out, which accounts for the correct potential in the middle of the channel and at the source and drain boundaries. Extensive comparisons between the analytical model and numerical results are carried out on the resulting conduction-band profiles, device characteristics and subthreshold swings. Different device geometries (gate length and oxide thickness) and morphologies (gate dielectric) are widely evaluated. This study confirms the effectiveness of DS-FETs as high-efficiency electronic switches, showing a minimum SS well below \(60\,\) mV/dec and a reasonable on-state current.