An analytical model for the subthreshold-slope (SS) of short-channel MOS transistors is presented in this paper. The expression for the subthreshold current, which is the basis of the subthreshold-slope, utilizes the concept of splitting of quasi-Fermi levels along the channel. The current model is based on the surface potential for short-channel devices where two-dimensional effects are incorporated by solving a pseudo-2D Poisson's equation. To arrive at a simple analytical expression, some approximations with proper explanation are made. The model results are compared with that of two-dimensional numerical simulation results using DESSIS of ISE TCAD, and a very good agreement between the two is found. © 2008 IEEE.