What is the highest maximum voltage for a high voltage FET or other transistor? I do not need to be able to buy it, just want to know the voltage it can handle.

I was searching the internet and found that I couldn't find any real high voltage FETs or other transistors. The highest I could find where between 3000 and 9000 V.

Are there actual transistors or MOSFETs for higher voltage out there for example in specialized machinery? The around 9000 V versions were experiments in universities.


3 Answers 3


For highest voltage per device you'll have to look into "vacuum state transistors" (ie, tubes) like Thyratrons, or even not-so-vacuum-filled valves like the Mercury Arc Rectifier, which is basically a thyristor. Voltage is somewhat unlimited since it depends on the length of the arc tube.

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At high voltage, you will find mostly thyristors and diodes, because the main application is switching and rectifying. An actual amplifier would require something like transistors, or triode/pentode tubes, but few are actually interested in 300kV output amplifiers...

What determines breakdown voltage is the length or thickness of the insulator, so for transistors this is limited to what is possible to manufacture and of course to what customers will buy. The whole point of semiconductors is that they're tiny so you can manufacture a lot of them cheaply on a wafer, but this results in insulation/creepage distances that are not compatible with hundreds of kV.

Theoretically it should be possible to build almost unlimited voltage triodes for that juicy Class-A sound. After all it's a glass tube, you can make it one meter long for the extra insulation distance. But that would be "special order".

  • \$\begingroup\$ okay, then I know enough for my case, since I wanted to know how a transistor actually worked on a deeper level to better use them which led me to develop my own cirquit for it instead of the often used approach of searching it(because designing it on yourself makes you truly understand it, and in my case if I know what I want something to do I can mostly design it within a second before finishing the mental design). so today I build my "transistor" which was also capable of a theoretical infinite voltage excluding strange effects. my prototype worked stable between 1kv and 30kv \$\endgroup\$ Mar 24, 2021 at 15:39
  • \$\begingroup\$ using it as a diode or rectifier would be more difficult but not impossible, however the polarity of such a diode might switch every time you fully remove power from the device. it is however stable in ac and simple to make. so I wanted to know if I should first make a showof of the high voltage "transistor" or directly publish it for all hobbyists. I'll go for that last one seeing the Mercury ark rectifier looks cool enough and works on such high voltages as well. so the only benefits my design has is it's simplicity and the materials used. \$\endgroup\$ Mar 24, 2021 at 15:42
  • \$\begingroup\$ also it has a side effect of generating virtual voltage which can also lead to actual voltage increase. amplification however does slightly work until it enters the point where it fully opens. since when I touch the trigger terminal and move my and close to one of the other 2 terminals that can open it depending on the distance. \$\endgroup\$ Mar 24, 2021 at 15:46
  • \$\begingroup\$ Interesting, how did you build it? \$\endgroup\$
    – bobflux
    Mar 24, 2021 at 16:04
  • \$\begingroup\$ I am currently working on putting it online including a demo. however since it is late in the night I can not yet finish it to avoid sound annoyance for others. I actually made 2 versions. the second is what I originally wanted to make, the first seems most stable to me. after putting it online I shall also explain how to make it. I will put it here as well for all those wanting something like that. \$\endgroup\$ Mar 24, 2021 at 21:58

For higher voltages series combinations of individual semiconductor devices (IGBTs and thyristors, usually) are used to handle things like a 275kV DC input that must be converted to 3-phase AC. Individual devices are probably in the 4-9kV range, you could probably find out with a bit of research.

There are some experimental devices in the 15kV range for SiC IGBTs but they may not be possible to buy.

If you have a specific problem to solve, you should look at solving it with easily available mature technology as a first step.

  • \$\begingroup\$ this shows me what I needed to know just like the other one. I wondered this question because I didn't fully understand how transistors actually worked on the material level, so I designed my own one and build it. I would personally consider it a king of cheap easily available material since it is actually so basic in principle that it can't go wrong I've personally ran my prototype from 1kv to around 30kv(partly virtual votage) since that is what my supply could deliver, it worked stable on those voltages. It should run to a unlimited voltage. \$\endgroup\$ Mar 24, 2021 at 15:32
  • \$\begingroup\$ so seen there exist things like it I'll directly bring it to the hobbyists so all can use it. otherwise I would first make something to show it of properly. \$\endgroup\$ Mar 24, 2021 at 15:33
  • \$\begingroup\$ You're right on the SiC. SiC is basically unobtanium unless you buy a wafer. I had to buy a wafer -.- \$\endgroup\$
    – b degnan
    Mar 25, 2021 at 1:25

So for those wanting to actually use something like that themselves. this: https://youtu.be/HIUtZSaXuow is the device I designed/made I still have to add its functional description. however, this holds enough information to reproduce it. and I think it is quite simple for people to come up with how it works for themselves + I am mostly visual-based which makes such things a lot harder to explain in words since I see the fields, etc.

but it is basically a simple transistor for high voltages which you can make from basically any materials. you have 2 terminals with a spark gap and one of 2 types of capacitor plate/material below it. you get some things like static push/pull energy flow which wants to keep going after stopping and a partly virtual voltage rise.

it is no diode-based transistor, but you can easily modify it to work as a diode. this requires a specific additional piece which in turn can turn as many of those in diodes as you like to.

This is not about commercially available stuff, but it is something any hobbyist could make if it needs a very high voltage transistor

  • 1
    \$\begingroup\$ That is not a transistor - "A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. ... It is composed of semiconductor material usually with at least three terminals for connection to an external circuit." At best you have made a couple of capacitors of tiny capacitance. \$\endgroup\$
    – Transistor
    Mar 26, 2021 at 21:41
  • \$\begingroup\$ @Transistor a MOSFET is a transistor as well, and in practical functionality, it is quite similar. 2 in/outputs and one terminal to trigger it or disable it. a voltage somewhere in between at a specific range can also be used to more accurately amplify. the device. Perhaps you might want to call it a FES (field effect sparkgab) instead, however that is not an official therm an this can be used basically like a transistor. you can even easily give it a diode property for rectification. so that it is different from what they taught you doesn't remove the functionality. but try it. \$\endgroup\$ Mar 27, 2021 at 6:54

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