A new extraction method which determines the saturation voltage of a small-geometry MOSFET directly from the measured data is proposed and investigated. In this method, a special function G is formed and the drain-source saturation voltage is identified as the voltage of the peak point in a plot of G vs the drain-source voltage. Since the method is based on a general device theory, it is virtually independent of any device model and quite versatile and applicable for all MOSFETs. In addition, no given device parameters or iterations are required in the method. To verify the new method, SPICE MOS models are used as a calculation example. Moreover, the method is also applied to various fabricated MOSFETs to determine the saturation voltage. It is found that the saturation voltage can be definitely determined without ambiguity and the determined saturation voltage is quite close to that from the optimal extractions. Thus the method can be incorporated into the parameter extraction and the device modeling for small-geometry MOSFETs.