It is shown that the classical threshold criterion based on critical band-bending leads to an inaccurate estimation of the linearly extrapolated threshold voltage V-Te of metal-oxide-semiconductor (MOS) devices. With the use of a properly defined and physically accurate condition for effective surface potential pinning, an approximate but explicit expression is derived for V-Te. Good agreement is obtained between the values of V-Te calculated using this expression and those extracted from the numerically simulated current-voltage characteristics of long-channel MOS field-effect transistors. Instead of increasing monotonically with the gate dielectric thickness, V-Te of an MOS device with a finite substrate doping concentration is found to exhibit a global minimum. (c) 2005 Elsevier Ltd. All rights reserved.