This work describes a new analytical MOSFET model for analog circuit simulation based on the charge-sheet model. The current equation consists of diffusion and drift components, therefore Ids is a smooth function of the applied voltages. Since the original charge-sheet model is valid only for long-channel transistors, it has been further developed to describe quarter-micron MOSFETs by introducing the lateral electric field Ey into the theory. The new model includes these field contributions self-consistently, and describes the drain current of MOSFETs from long to quarter-micron channel lengths with a single model parameter set without discontinuities in derivatives of the drain current Ids. The mobility reduction due to Ey is described by an empirical equation with physical parameter values taken from literature. Only two fitting parameters, the impurity scattering and the surface roughness scattering in the mobility equation, are added to the physical parameters. The subdiffusion lengths are also taken as fitting parameters. Though the new model reduces the number of fitting parameters totally to four, it reproduces measured Ids excellently for MOSFETs with all channel lengths. The model has been included in the parameter extraction program JANUS, which extracts model parameters automatically. The algorithm for parameter extraction is summarized.