Transistors — Martin Stellinga

Transistors make the world go round. Well, sort of. They make all our electronics function. Everything has a chip in it these days, and chips all have transistors in them. But how do they work?

The basics

I talked about the ultimate application of transistors last week, but how do they work?

A transistor is a so-called semiconductor. A conductor can conduct an electric current with little loss of power. An insulator cannot conduct a current. And a semiconductor can conduct a current under certain conditions. Meaning under certain conditions current flows through it, and under other conditions it doesn’t.

The magical thing about a transistor is that the ‘conditions’ under which the current flows are controllable by… an electrical current. Meaning it can be used like a switch. It can also amplify electrical signals.

It’s that switching property that makes them the basis of modern electronics. You see, because a transistor is a switch which can be controlled with electrical current, the output of a transistor can be used to control another transistor. And that opens up a whole range of options.

Gates

Wire together a couple of transistors and you can create a logic gate. I won’t go into the schematics — maybe some other time — but a logic gate takes one or two inputs, and generates an output based on a logical operation. As input it uses currents, which is either high or low, meaning 1 or 0 — wait… 1 and 0… Yes, computers.

Sound complex? Okay, an example: the NOT gate.

A NOT gate has one input and one output. If a 0 goes in, a 1 comes out. If a 1 goes in, a 0 comes out. So a logical NOT operation (the output is the opposite of the input). See, not that complex (and wiring up a transistor to do this is actually pretty simple too).

An AND gate has two inputs and one output. The output is 0, unless input A and B are 1.

And so on. There are NOT gates, AND gates, OR gates, NAND gates, NOR gates, XOR gates, and XNOR gates. I’m not going to go into all of them. But those gates are what makes computer do there thing.

Next step: wire several of these gates together, using outputs of some to influence others. Then introduce a so-called clock pulse, which synchronizes this process of logical transformation. Stack millions of these together, then use a clock that pulses millions of times per second, and voila. You can perform a million times a million operations per second, and before you know it you’ve got yourself an iPhone.

Side note, the clock pulse is what determines the ‘megahertz’ and ‘gigahertz’ denomination of your computer. Now you know what that means.

How do transistors work?

Okay, let’s look at the physics. You take a very pure insulating material, then ‘dope’ it with certain other materials. This doping creates microscopic semi-conductor materials.

The earliest transistors use two types of semi-conductors resulting from doping: n-type and p-type semi-conductors. The first has free electrons, and the second electron deficits (holes). By sandwiching those together, P-N-P or N-P-N, you can create so-called BJT transistors (the first as a switch and the second as an amplifier). The combination of the holes and free electrons make it function.

A newer type of transistor is the MOSFET. Those are based on oxidizing metals. An oxidised layer on top of a non-oxidised base creates the switch/amplifier effect. These ones are used in CPUs and GPUs in a modern computer and created by putting a wafer in a stepper device.

Sound complicated? Yeah, it requires quite a lot of knowledge about chemistry and physics and how electrical currents work at the atomic level. And I’m glossing over the details.

Suffice it to say: you take a base material, and create microscopic changes to create a very tiny transistor. And by ‘tiny’ I mean, nanometer-scale. That way you can create millions of the tiny buggers on a processor.

Conclusion

Transistors are one of the most important inventions of the previous century. And I hope I was able to get across some of the basics, while also imparting how much they rely on a combination of deep understanding of physics and modern feats of engineering. There’s a reason they didn’t have computers in the middle ages.

But since a hundred years we’ve been slowly tackling the engineering and physics, which has brought us to things like Assassin’s Creed Black Flag, which I discussed last week. And now you can maybe appreciate what feats computers and these games really are.

Originally published at https://martinstellinga.com on May 8, 2026.