Definition
A type of transistor in which the control electrode (the gate) is electrically isolated from the main current-carrying channel by a thin layer of insulating material. A small voltage applied to the insulated gate creates an electric field that controls the flow of current between the other two terminals (source and drain), without the gate itself drawing any meaningful current. The most common form of IGFET is the MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor).
Plain English
An electronic switch or amplifier where one terminal controls the flow of electricity through the device using only an electric field, not direct contact. Because that controlling terminal is insulated, it uses almost no power to do its job.
Context Anchor
Seen in aircraft electrical and avionics maintenance material, especially in power supplies, regulators, control units, and solid-state switching circuits.
Derivation
Built from its function: 'Insulated Gate' means the controlling terminal is separated from the rest of the circuit by an insulator. 'Field Effect' means the device works by the effect of an electric field rather than by current flowing into the control terminal. 'Transistor' comes from 'transfer resistor,' the original name for a semiconductor device that transfers a signal across a resistive junction.
Why Pilots Care
Pilots do not interact with IGFETs directly, but they are the building blocks of nearly every modern avionics box, glass cockpit display, and digital engine controller in the aircraft. Understanding the term helps when reading maintenance manuals or troubleshooting documentation.
Analogy
Think of it like a water valve controlled by a touch sensor. The touch signal does not become the water flow; it only tells the valve how much flow to allow.
Intuition Check
Do not read gate as a physical door or insulated as heat insulation. Here, the gate is an electrical control point, and insulated means electrically separated from the current path it controls.
Example Sentence 1
The avionics technician explained that the failed display unit contained thousands of insulated gate field effect transistors on a single chip.
Example Sentence 2
During an avionics bench test the technician verified that each insulated gate field effect transistor responded correctly to gate voltage changes.