To accurately measure MOS inversion-layer mobility, the carrier density is evaluated by integrating gate-source capacitance from the gate voltage (V-G0) where the inversion carrier density is considered to be zero. The ambiguousness in V-G0 determination, therefore, becomes error in the measurement of inversion-layer mobility. This short note shows that defining V-G0 as the threshold voltage minus mS, where S is subthreshold slope and m greater than or equal to 5, can suppress the ambiguousness in V-G0 determination. (C) 2003 Elsevier Science Ltd. All rights reserved.