For an n-channel enhancement type MOSFET, if the source is connected at a higher potential than that of the bulk,the threshold voltage V_T of the MOSFET will

VT is a function of several components, most of which are material constants such as the difference in work-function between gate and substrate material, the oxide thickness, the Fermi voltage, the charge of impurities trapped at the surface between channel and gate oxide, and the dosage of ions implanted for threshold adjustment. From the above arguments, it has become clear that the source-bulk voltage VSB has an impact on the threshold as well. Therefore, whenever there is an increase in the source-bulk voltage, threshold voltage also increases.