Transistor

In simple terms

A transistor is a tiny electronic switch. A small voltage on one terminal controls whether current flows between the other two. Modern CPUs contain tens of billions of them, etched onto a fingernail-sized chip and switching billions of times per second.

More detail

The dominant type today is the MOSFET (metal-oxide-semiconductor field-effect transistor). A voltage on the gate creates a conductive channel between the source and drain.

Two MOSFET flavours combine in CMOS logic — the foundation of all modern digital chips: n-type and p-type transistors paired so that almost no current flows except when switching, keeping power consumption manageable at billions of devices.

Key trends:

• Moore’s Law observed that transistor count doubles roughly every two years. It held for ~50 years; in the late 2010s it slowed.
• Process nodes (“5 nm”, “3 nm”) describe the manufacturing generation. The numbers are largely marketing now — actual features are larger.
• 3D structures (FinFET, GAAFET) replaced flat MOSFETs once features got too small.

Modern AI accelerators and CPUs measure die area by billions of transistors. An Apple M-series chip has ~20–30 billion; a top-end Nvidia GPU has 80+ billion.

Why it matters

Every digital device — phone, laptop, microwave, satellite — runs on patterns of transistors switching on and off. They are the physical substrate of computing.

Real-world examples

• The first commercial transistor radio (1954) had four transistors.

• A modern flagship phone SoC has ~20 billion transistors in a few hundred square millimetres.

• A single failed transistor among billions usually has no observable effect, thanks to error correction and redundancy.

• Apple’s M4 chip packs roughly 28 billion transistors into a die smaller than your thumbnail, on TSMC’s 3 nm process — a density that took 70+ years of scaling to reach.

Common misconceptions

• “Smaller process = smaller transistor.” Smaller process nodes pack more transistors and consume less power per switch, but the headline number is no longer the physical gate length.
• “Transistors are analog.” They have analog physics; in digital chips they’re driven to behave as switches.

Learn next

What transistors combine into: logic gates. The big assemblies of gates: CPU.