Pinch-off voltage is a term used in the context of transistors, and it can refer to one of two different characteristics depending on the type of transistor.

• In insulated-gate field-effect transistors (IGFET), pinch-off refers to the channel pinching that leads to current saturation behavior under high source-drain bias. In this case, the pinch-off voltage is the value of Vds when drain current reaches a constant saturation value.

• In junction field-effect transistors (JFETs), pinch-off refers to the threshold voltage below which the transistor turns off. At gate-to-source voltage VGS = Vp, called the "pinch-off" voltage, the channel width is reduced to zero because all the free charge has been removed from the channel. Accordingly, for a fixed drain-to-source voltage, the drain current will be a function of the reverse-biasing voltage across the gate junction.

Therefore, the pinch-off voltage is the voltage at which the channel is pinched off, and the current becomes constant or the transistor turns off.