[1] JFETs are three-terminal semiconductor devices that can be used as electronically controlled switches or resistors, or to build amplifiers.

Unlike bipolar junction transistors, JFETs are exclusively voltage-controlled in that they do not need a biasing current.

By applying a reverse bias voltage to a gate terminal, the channel is pinched, so that the electric current is impeded or switched off completely.

JFETs are sometimes referred to as depletion-mode devices, as they rely on the principle of a depletion region, which is devoid of majority charge carriers.

However, materials science and fabrication technology would require decades of advances before FETs could actually be manufactured.

[3] During the 1940s, researchers John Bardeen, Walter Houser Brattain, and William Shockley were trying to build a FET, but failed in their repeated attempts.

[4] Japanese engineers Jun-ichi Nishizawa and Y. Watanabe applied for a patent for a similar device in 1950 termed static induction transistor (SIT).

[4] High-speed, high-voltage switching with JFETs became technically feasible following the commercial introduction of Silicon carbide (SiC) wide-bandgap devices in 2008.

Due to early difficulties in manufacturing — in particular, inconsistencies and low yield — SiC JFETs remained a niche product at first, with correspondingly high costs.

The current also depends on the electric field between source and drain (analogous to the difference in pressure on either end of the hose).

The JFET shares this constant-current characteristic with junction transistors and with thermionic tube (valve) tetrodes and pentodes.

Constriction of the conducting channel is accomplished using the field effect: a voltage between the gate and the source is applied to reverse bias the gate-source pn-junction, thereby widening the depletion layer of this junction (see top figure), encroaching upon the conducting channel and restricting its cross-sectional area.

The symbol may be drawn inside a circle (representing the envelope of a discrete device) if the enclosure is important to circuit function, such as dual matched components in the same package.

The JFET has higher gain (transconductance) than the MOSFET, as well as lower flicker noise, and is therefore used in some low-noise, high input-impedance op-amps.

[15] The current in N-JFET due to a small voltage VDS (that is, in the linear or ohmic[16] or triode region[7]) is given by treating the channel as a rectangular bar of material of electrical conductivity