A new unified current-voltage model is developed for long-channel nMOSFET. This new model is based on the unified charge control model (UCCM), which agrees very well with quantum-mechanical calculation results assuming two-dimensional electron gas as well as with experimental capacitance-voltage measurements for the inversion layer formed at the Si/SiO2 interface on (100) surface. Combining UCCM with newly proposed universal mobility model at room temperature, we develop a new continuous I-V model which shows excellent agreement with the experimental data for the entire operating regions of gate, drain, and substrate bias voltages.