JFET:Junction field effect transistor is a three terminal semiconductor device in which current conduction is by one type of carrier (i.e., electrons or holes.)
The JFET was developed about the same time as the transistor but it came into general use only in the late 1960s. In a JFET, the current conduction is either by electrons or holes and is controlled by
means of an electric field between the gate electrode and the conducting channel of the device. The JFET has high input impedance and low noise level.
Constructional details : A JFET consists of a p-type or n-type silicon bar containing two pn junctions . The bar forms the conducting channel for the charge carriers. If the bar is of n-type, it is called n-channel JFET and if the bar is of p type, it is called a p-channel JFET. The two pn junctions forming diodes are connected *internally and a common terminal called gate is taken out. Other terminals are source and drain taken out from the bar . Thus a JFET has essentially three terminals viz.