Tetrode transistor

Atetrode transistoris anytransistorhaving four active terminals.

Early tetrode transistors

There were two types of tetrode transistor developed in the early 1950s as an improvement over thepoint-contact transistorand the latergrown-junction transistorandalloy-junction transistor.Both offered much higher speed than earlier transistors.

Point-contact transistor having two emitters. It became obsolete in the middle 1950s.
Modified grown-junction transistor or alloy-junction transistor having two connections at opposite ends of the base.^[1]It achieved its high speed by reducing the input to outputcapacitance.It became obsolete in the early 1960s with the development of thediffusion transistor.

Dual emitter transistor, used in two-inputtransistor-transistor logicgates
Dual collector transistor, used in two-outputintegrated injection logicgates
Diffused planar silicon bipolar junction transistor,^[2]used in someintegrated circuits.This transistor, apart from the three electrodes (emitter, base, and collector), has a fourth electrode or grid made of conducting material placed near the emitter-base junction from which it is insulated by a silica layer.
Field-effect tetrode

^Wolf, Oswald; R. T. Kramer; J. Spiech; H. Shleuder (1966).Special Purpose Transistors: A Self-Instructional Programmed Manual.Prentice Hall.pp. 98–102.
^U.S. patent 4,143,421-Tetrode transistor memory logic cell,March 6, 1979. Filed September 6, 1977.