The collocation method has been applied to derive a new SPICE (Simulation Program with Integrated Circuit Emphasis)-compatible non-quasi-static MOS (metal-oxide-semiconductor) transient model. Contrasting to the conventional approximation methods, the collocation method is simple for the model derivation and efficient in optimizing the variables of the continuity equation. The derived model is fully physics-based in that all the transient currents are directly expressed by only physically meaningful, optimized quantities. The model adequately predicts transient currents in the bias region such as the weak inversion region where conventional models show numerical difficulties.