An analytic non-quasi-static (NQS) long-channel MOSFET model has been derived and implemented in SPICE. It is based on an approximate solution to the nonlinear current-continuity equation in the channel. The model includes the large-signal transient and the small-signal ac analyses, although only the transient model is reported in this paper. Comparisons have been made between this model and the 1-D numerical solution to the current-continuity equation, 2-D device simulation (PISCES), and the quasistatic (QS) results. The channel-charge partitioning scheme in the charge-based QS models is shown to be inadequate for the fast transient. This model does not use a charge-partitioning scheme and the currents are dependent on the history of the terminal voltages, not just the instantaneous voltages and their derivatives. For the slow signals (compared to the channel transit time), the NQS model is reduced to the quasistatic 40/60 channel-charge partitioning scheme. The CPU time required for this model is about two-to-three times longer than that of conventional MOSFET models in SPICE.