We clearly know that the accuracy of a device model in predicting device characteristics is dependent on the correct parameters of the model. In this paper, we completely investigate how to determine the threshold voltage of MOSFET devices. In order to succeed in getting threshold voltage, we present a new physically based method for measuring the threshold voltage of MOSFET devices. This novel method, called the bulk charge varying (BCV) method, is based on the drain current to include the bulk charge variation from the source end to the drain end. The BCV method will be a new accurately technique for experimentally extracting the threshold voltage of MOSFET devices.