Pinch-off voltage is the voltage at which a field-effect transistor’s channel becomes so narrow that the drain current stops increasing much and the device enters saturation. In simple terms, it’s the point where the transistor starts acting like a current source rather than a resistor.

Quick Scoop

  • In a JFET , pinch-off is commonly used to describe the voltage where the channel closes enough to nearly stop current flow.
  • In a MOSFET , the term is often used for the point where the channel pinches near the drain and current saturates as drain-source voltage increases.
  • Some sources use pinch-off voltage and threshold voltage differently depending on the device type, so the exact meaning depends on whether you’re talking about a JFET or MOSFET.

Simple idea

Think of water flowing through a hose. As the channel pinches off, the hose gets so constricted that increasing the downstream pressure does not increase flow much anymore. That is why the current levels off in the saturation region.

Why it matters

  • It helps define the operating regions of FETs.
  • It is important in amplifier and switch design because it affects current control and output behavior.
  • It is not always the same as the “turn-on” threshold, especially when comparing different transistor types.

If you want, I can also explain pinch-off voltage in JFET vs MOSFET with a tiny diagram-style example.