In order to alleviate the influence of fluctuation of experimental data from noise and errors of measurement systems, a differential smoothing technique has been introduced into the extraction of threshold voltage of MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). The results show that the transconductance versus the gate voltage (g(m)-V-g) curves could be smoother when the smoothing rank grows. A criterion to seek the best optimal fitting curve, named as the mismatch rate, has been proposed to obtain the threshold voltage parameter stably and automatically. This technique will contribute to the analysis of the characteristics of MOSFET and the designation of the integrated circuits. (C) 2012 Elsevier Ltd. All rights reserved.