The Subthreshold conduction or the subthreshold leakage or the subthreshold drain current is the current

Electric current

Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...

 that flows between the source and drain of a MOSFET

MOSFET

The metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...

 when the transistor

Transistor

A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

 is in subthreshold region, or weak-inversion region, that is, for gate-to-source voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

s below the threshold voltage

Threshold voltage

The threshold voltage of a MOSFET is usually defined as the gate voltage where an inversion layer forms at the interface between the insulating layer and the substrate of the transistor. The purpose of the inversion layer's forming is to allow the flow of electrons through the gate-source junction...

. The subthreshold region is often referred to as the weak inversion region. The terminology for various degrees of inversion is described in Tsividis.

In digital circuits, subthreshold conduction is generally viewed as a parasitic leakage in a state that would ideally have no current.