The difference in MOSFET threshold voltages caused by the difference in the extraction method is studied, by measuring and analyzing its dependencies on channel length, substrate voltage and drain voltage. It is found that the standard deviation of the difference between threshold voltages caused by the difference in the extraction method is less than that of the threshold voltage itself in a wafer. The dependencies of the threshold voltage on channel length, extracted from the drain current data around the threshold voltage, however, show different behavior from those extracted from the drain current data only in the subthreshold region or only in the ON region. It is considered that "channel-length modulation" causes this different behavior and, therefore, that those extraction methods are not desirable.