A closed form analytical expression is derived to predict the threshold voltage of a narrow-width MOSFET. The present calculation utilizes the Fourier transform technique to analyze the voltage over the width cross section of the basic MOS device structure. No fitting parameter with experimental data is necessary because the fringe electric field is calculated directly from the relevant physical parameters to deduce the threshold voltage. The dependence of threshold voltage on channel width and substrate bias thus obtained is in reasonable agreement with experimental and numerical results. The effects of field doping and field oxide thickness on the threshold voltage are also taken into consideration. A comparison is made of the present analytical expression for threshold voltage with that, based on an adjustable weighting factor, of earlier analytical models.