Threshold voltage

The threshold voltage, commonly abbreviated as V_th or V_{GS (th)}, of a field-effect transistor (FET) is the minimum gate-to-source voltage differential that is needed to create a conducting path between the source and drain terminals.

For an nMOS device at gate-to-source voltages above the threshold voltage ((V_GS > V_th) but still below saturation (less than "fully on", (V_GS − V_th) > V_DS), the transistor is in its 'linear region', also known as ohmic mode, where it behaves like a voltage-controlled variable resistor.

When referring to a junction field-effect transistor (JFET), the threshold voltage is often called "pinch-off voltage" instead. This is somewhat confusing since "pinch off" applied to insulated-gate field-effect transistor (IGFET) refers to the channel pinching that leads to current saturation behaviour under high source–drain bias, even though the current is never off. Unlike "pinch off", the term "threshold voltage" is unambiguous and refers to the same concept in any field-effect transistor.