This paper provides a unified and process-independent MOSFET model for accurate prediction of the I-V characteristics and the threshold voltages of narrow-gate MOSFET's. It was developed based on several enhancements of the SPICE2 LEVEL3 MOS model and our previous subthreshold I-V model. The expressions achieved for the drain current hold in the subthreshold, transition, and strong inversion regions. In the strong inversion region, five parameters are used in the I-V formulation, while in the subthreshold region, two parameters are used. A continuous model in the transition region is proposed using a new scheme that will ensure that both the current and conductance are continuous and will not cause convergence problems for circuit simulation applications. All of the modeled parameters are taken from experimentally measured I-V characteristics and preserve physical meaning. A new and simple threshold voltage model of narrow-gate MOSFET's with implanted channel is also successfully developed. Comparisons between the measured and modeled I-V characteristics show excellent agreement for a wide range of channel widths and biases. The developed model is well suited for circuit simulation in SPICE.