What Is a MOSFET?

A MOSFET is a type of transistor used to switch or amplify electronic signals. The term MOSFET stands for Metal-Oxide Semiconductor Field-Effect Transistor. MOSFETs serve as a cornerstone component in modern electronics, offering high efficiency and fast switching performance. A MOSFET symbol contains four terminals:

Gate

Source

Drain (Note: The original text mistakenly used “Direnç/Direnç = resistance”; the correct terminal name is “Drain” in MOSFET terminology.)

Body (substrate in some symbol representations)

The Gate terminal controls the current flow between Source and Drain. When no voltage is applied to the Gate, the channel remains non-conductive (for enhancement-mode MOSFETs). When appropriate voltage is applied, the channel becomes conductive, allowing current to flow.

What Does a MOSFET Do?
MOSFET driver circuits are used in a wide range of applications—from power management to signal transmission. MOSFET devices can operate in two modes:

Depletion Mode (Normally ON): The channel conducts by default. To turn it OFF, voltage must be applied to the Gate.

Enhancement Mode (Normally OFF): The channel does not conduct by default. To turn it ON, voltage must be applied to the Gate.

N-Channel MOSFETs use electrons as primary carriers and provide higher performance due to their superior mobility. P-Channel MOSFETs use holes (positive carriers) and are typically slower and less efficient than N-Channel models. N-Channel MOSFETs require positive Gate-to-Source voltage to turn ON, while P-Channel MOSFETs require negative Gate-to-Source voltage to turn ON.

MOSFET Working Principle
The MOSFET working principle is based on the electric field generated at the Gate terminal:

When voltage is applied to the Gate, an electric field forms in the channel region.

In N-Channel MOSFETs, positive Gate voltage attracts electrons into the channel, making it conductive and enabling current to flow from Drain to Source.

In P-Channel MOSFETs, negative Gate voltage attracts positive charge carriers (holes) into the channel, making it conductive and enabling current to flow from Source to Drain.

When no voltage is applied to the Gate, the channel closes and stops conduction.

Where Are MOSFETs Used?
MOSFET devices are widely used in:

Automotive electronics

Telecommunications

Consumer electronics

High-frequency switching circuits

Power supply units

Low-voltage motor control circuits

DC-DC converters

Measurement instruments (voltmeter, ohmmeter, multimeter)

How to Measure a MOSFET
MOSFET health and performance checks can be performed using:

Multimeter (Diode Mode): Gate, Drain, and Source terminals are tested for continuity and resistance behavior. Drain-to-Source resistance must differ between ON/OFF states.

Oscilloscope (Dynamic Test): Used to evaluate switching speed and signal response.

Terminal Resistance Check: If Gate-to-Source resistance is abnormally low, MOSFET may be faulty.

Thermal Test: If excessive overheating is detected during operation, MOSFET may be faulty.

MOSFET Types
MOSFET variants are mainly categorized as:

N-Channel MOSFET: Higher current capacity, faster switching, more efficient.

P-Channel MOSFET: Uses holes as carriers, lower switching speed, lower performance compared to N-Channel.

Based on default conduction state:

Depletion Type (Normally ON)

Enhancement Type (Normally OFF) (most commonly used MOSFET type)

MOSFET Pricing
MOSFET driver circuit pricing varies depending on product features, material quality, and supplier. The most suitable, high-quality, and cost-effective MOSFET models can be found at Empa Store, which serves as an official distributor for many global electronics brands in Türkiye. You can review MOSFET price ranges on Empa Store’s online shop and select the best model for your needs and budget.