So let's say that we never figure out how to purify silicon and germanium to the levels required to make transistors. This would readily happen in a technical culture that wanted clear and quick results from research projects. Bell was doing pretty basic research when it started.

  • What communication abilities would we have or not have? Radio? TV?
  • Would we invent analog computers? Or we just not have computing?
  • What technologies and sciences have been different? Would we have landed on the moon? Would we still study cryptography and computer science?
  • How would society be different?
  • $\begingroup$ This question is perfectly answerable and i see no reason to close. $\endgroup$
    – Jorge Aldo
    Commented Apr 11, 2015 at 20:07
  • $\begingroup$ Do you include diodes or just treasuries? $\endgroup$
    – RoboKaren
    Commented Apr 11, 2015 at 20:16
  • $\begingroup$ a diode valve can be miniaturized just as much as a triode. $\endgroup$
    – Jorge Aldo
    Commented Apr 11, 2015 at 20:17
  • 1
    $\begingroup$ @RoboKaren Anything made out of semiconducting material. For example, it would be impossible to build silicon statues in this society. $\endgroup$ Commented Apr 11, 2015 at 20:42
  • $\begingroup$ Semi-conductor is a pure insulator intentionally contaminated (see doping) so that under a specific condition(s) it becomes a switch (see quantum tunneling) and without these semi-conductor you'll be trawling your smartphone as all the switches is actually vacuum tubes (each around size of 1.5L mineral water bottles) I'm pretty sure you would rather everything to scale down to fit you palm, excepts where such items involve reproductive systems. (Adopted from Jorge Aldo's answer) $\endgroup$
    – user6760
    Commented Apr 12, 2015 at 0:02

6 Answers 6


You would probably want to refine your question before answering. The amount of handwavium you would have to expend is pretty intense.

Consider that "semiconductor" is a pretty wide net. Wikipedia has a nice list of semiconductors. You'll probably miss some of these materials in your day to day life:

  • Silicon - this makes up 15% of the earth, and is pretty darn important for making sand (silicon dioxide). I expect beach vacations would be less enjoyable without this semiconducting material
  • Diamond - yep, sorry girls. Diamond is a semiconductor, with a bandgap of 5x that of silicon, and really nice chemical and thermal properties. We'll have to find something else to be forever on your ring.
  • Sulfur - So no one will miss this stinky compound, which is a semiconductor itself. However, if I may quote wikipedia's page on Sulfur, " Sulfur is an essential component of all living cells. It is the seventh or eighth most abundant element in the human body by weight, being about as common as potassium, and a little more common than sodium or chlorine." Clearly life will be different without this compound

So, lets back off and try a different approach. Let's handwave physics to no longer have these band gaps needed for semiconductors. Unfortunately, this will render the question rather unanswerable. When you start messing with the laws of physics, it gets hard to predict what will happen. It's hard to rewrite something like "how electrons work" without unintended side effects. The end result will be world which resembles ours in the same way the bottom corner of this picture of a lemur when played through a loudspeaker using QAM modulation resembles this million dollar Ferarri... which is to say, one does not resemble the other in the least.

So lets take a different approach. Rather than try to wipe out semiconductors, what I think you're really trying to do is prevent us from building computers using them. This is a handwave activity. Perhaps we just don't like semiconductors, or maybe there's a religious edict against them. Maybe each semiconductor has a spirit, and we do not want to offend it. Anything goes. So let's see what we can answer:

What communication abilities would we have or not have? Radio? TV?

Radio would absolutely exist. Radio was quite a mature technology long before semiconductors came along. Vacuum tubes proved more than sufficient for radio. Television also predates the transistor (which I'm assuming is the interesting point in time for your search). So both of these could exist.

Would we invent analog computers? Or we just not have computing?

Digital computing is totally possible without semiconductors, and analog computing is totally possible with semiconductors (we do it in ASICs all the time). There would probably be more of a focus on special-purpose computing because we wouldn't have the horsepower to do much of the generic stuff we do today. Accordingly, I would expect to see more analog sides to things, because many of the interesting problems to solve involve analog components to them.

What technologies and sciences have been different? Would we have landed on the moon? Would we still study cryptography and computer science?

Almost certainly not. Landing on the moon was an amazing feat, even with transistors and core-memory. Trying to do that with the heavy weight of vacuum tubes... we just wouldn't have bothered. Cryptography would still exist, but it would be VERY different. Cryptography existed long before semiconductors took over, but the modern fascination with things like prime factorization and such would probably not occur. I would expect computer science would fade away, replaced with computer art. With more special purpose computers out there, managing them would be an art, not a science.

How would society be different?

Different. This is really too broad of a question. The whole fun bit about society is how unpredictable it is. Trying to rewrite 50-60+ years and predict exactly where it ends up is virtually impossible. Maybe there was no WWII. Maybe Germany won WWII. Maybe Steve Jobs planted an orchard. The futures are literally limitless.

  • $\begingroup$ How reasonable would "we just never thought of using semiconductors in computers" be? Also, what about the internet? $\endgroup$ Commented Apr 11, 2015 at 23:22
  • 2
    $\begingroup$ sorry but you are wrong about being impossible to make a computer light enough for spaceship use out of valves. $\endgroup$
    – Jorge Aldo
    Commented Apr 11, 2015 at 23:28
  • 1
    $\begingroup$ Making semiconductors expensive would be hard (they are just really nice sand, after all). However, making ICs really expensive might be possible. Photolithorgaphy was essential for mass production of ICs. If any one step in photolithography was broken by you, ICs might have to be produced by less bulk-processing means. $\endgroup$
    – Cort Ammon
    Commented Apr 12, 2015 at 0:23
  • 1
    $\begingroup$ @JorgeAldo Yes, you can, but I believe that would make them much more expensive. $\endgroup$
    – Cort Ammon
    Commented Apr 12, 2015 at 7:02
  • 1
    $\begingroup$ @MartinSchröder color TV existed (in the US) in the 1950s, and was based completely on vacuum tubes. $\endgroup$
    – RonJohn
    Commented Aug 13, 2018 at 12:26

You can do everything with valves or microrelays. But, without semiconductors you cannot do microprocessors. Miniaturization cannot take place so you wont see portable devices. You can integrate and miniaturize valves :

miniature valve

We cannot know how much more could thermionic valves be miniaturized or integrated. Transistors provided a easier path and that was followed instead.

With this in mind you can build the following:

  • Digital and analog computers.
  • Radios and TV.
  • Limited cellphones (handheld radio transceivers)
  • Analog circuitry.

Due to the lower reliability of valved circuits, you would not want to do:

  • Eletronic engine controls. (You can control a engine with a valved analog circuit, but valves are too much sensible to vibration)
  • Too complex life support systems.

You cannot do :

  • Smartphones.
  • Personal computers.
  • MPEG or other digial algorithmm compression. So no digital TVs.
  • Anything that depends on miniaturization.

  • EDIT -

Decided to edit my post because of a lot of answers with wrong ideas being posted:

You can do computers with vacuum tubes (called valves in UK). The computers can be quite complex. The only difference between a modern computer and a computer made with vacuum tubes is scale. Transistors are made today on nanometer scale while the smallest valve could be made at milimeter scale. This means a lot of things.

1 - The less integration increases path delays amont units. This means that there will be a upper limit on the maximum speed of the computer. And this limit will be much smaller than the limit imposed on current silicon-on-sapphire designs. Integration means that all devices that compose a microprocessor are micrometers away at most. 2 - The use of a heat source to make thermionic emission possible means that valves have a much larger thermal footprint than semiconductors. This means that large designs will present a thermal management challenge. 3 - They use a lot more power than semiconductors.

This means that computers will tend to be centralized and used as a kind of utility, just like your phone, your water and your eletricity. What you would have at your home would be probably a dumb terminal made out of simple valved circuits. Multitasking at the central computer means that a lot of people can and do stay connected at the same time. Maybe the generally smaller bandwidth disponible will preclude the development of graphical applications. Etc. In other words, computers will gravitate mainframe era designs.

About modems, yes, you can do modems with vacuum tubes. What must be understood about vacuum tubes is that they have the behaviour of a cmos transistor. BUT, they operate at higher voltages and their size is much bigger than the usual CMOS transistor. This means that anything that can be done with CMOS transmistors might be possible using vacuum tubes, minus the miniaturization. You can do ASK/FSK/PSK modems with vacuum tubes. You can do analog to digital converters. etc. You can do precision guidance systems.

For one, the missiles and radar on the MiG-25 (and other aircraft of the era) where fully vacuum tube based. Guiding a missile across a radar beam is precision guidance (just not fire and forget, but its not all that hard to build radar homing active guidance missiles with vacuum tubes).

About TV. Analog color tv is designed around backward compatibility with analog BW tv. This placed certain constraints on the signal quality. Color information is carried in a phase modulation embedded into the luminance signal of the original BW tv. This means that a limited bandwidth was divided between two signals. Luminance gets most of the bandwidth. But, provided that there was no transistors disponible and people wanted a higher resolution TV standard, you can increase resolution by increasing the bandwidth disponible. This means that the usually 6mhz color tv channels used in analog NTSC tv might be enlarged to 12mhz or more to include a separated color carrier. This alone can increase the perceived resolution of color tvs. Thats not impossible, it was not economical at the time the color tv standards where created.

Regarding satellites, most satellites are operated as dumb repeaters. Eletronics inside the satellites are at premium. Space is constrained by thermal management needs and the general cost of launch that is proportional to weight. Being at 300km above ground or more means that repair on-site is impossible or quite costly (see hubble space telescope). This means that eletronics inside the satellites are bare, just enough to repeat signals. You can include beamforming systems on the sats to increase the bandwidth disponible by employing spatial multiplexing, and the algorithmns involved in such beamforming might very well be beyong vacuum tube capabilities, but, non-beamforming sats can be and are still usefull. So, miniaturized valves or not, you can still build satellites. A side not is about a computer capable of guiding the apollo missions. Yes, it can be done. Usually if you cannot treat some problem digitally you can do it in a analog computer. So, provided that you can miniaturize valves to 30mm scale, you can very well build a small computer capable of integrating speeds and other variables needed to space travel. You can beam a couple of tight radio wave beams towards the moon, you can do WW2 era navigation with radio navigation aids. You might be surprised what can be achieved with vacuum tube technology. You might be interested in the battle of beams wich ocurred in WW2. Collossus and other computers of the time might provide a hint how computers would evolve if vacuum tubes where the only option.

  • $\begingroup$ How far along would digital computers be? Could they support space travel? How advanced of calculations? $\endgroup$ Commented Apr 11, 2015 at 19:59
  • $\begingroup$ Pretty hard to predict, but, yes, you can strap a valved computer into a spacecraft. But it wont look how they usually look. A lot of computer science theory still in use today was developed during the early computer era. $\endgroup$
    – Jorge Aldo
    Commented Apr 11, 2015 at 20:02
  • 1
    $\begingroup$ @PyRulez: The problem is reliability. It's probably o.k. for ballistic missiles, but not for manned missions. $\endgroup$ Commented Apr 13, 2015 at 22:17
  • $\begingroup$ Look at the Librascope LGP series of computers that actually existed in the 1950 to see what could easily be done with vacuum tubes regarding digital computers (these used semiconductor DIODES but not semiconductors as amplifying elements, and would not have NEEDED the semiconductor diodes.). If one really cared about miniaturizing, using technology like the subminiature tubes shown in other posts, such a machine could likely be scaled down to a cubic foot. $\endgroup$ Commented Sep 9, 2016 at 7:58
  • $\begingroup$ @rackandboneman did you really read the post ? $\endgroup$
    – Jorge Aldo
    Commented Sep 10, 2016 at 12:46

Technological development would be delayed by some amount. How much exactly is hard to predict.

Alternative methods would be discovered. Miniaturized vacuum tubes would be the first development, perhaps followed by vacuum tube integrated circuits.

Eventually we would discover a way to make transistor-like devices without semiconductors. For example carbon nanotubes can be used and optical transistors are in development also.


You might end up miniturizing vacuum tubes to the size of grains of sand. That might evolve into technology for switches that is not "vacuum" but still based on ballistic electrons or non-linear media that's not the way semiconductors work. Classic ionization, Hall effect, magnetic beads re-configuring conductive pathways...

Semiconductors allow us to work on the scale of atoms, limited by the S/N of quantum effects. The other things would not be as small in scale, but still orders of magnitude smaller and more reliable than old vacuum tubes.

Core memory does not depend on semiconductors, and I've seen a module that contained rows of tubes in addition to the screens of ferrite cores. A small number of tubes for signal amplification and simple logic gates, but a few dozen tubes service thousands of cores. What if the cores were wired in a fancier way to implement the logic, like a cellular automata (later: I’ve seen this on youtube! Core logic actually predates its use as memory!)? Point is, other tech could evolve to do computation that still uses just a few tubes for support.


Radio, TV and microwave radar were all developed and implemented with vacuum tubes before transistors. So we would definitely have these things.

Eliminating semiconductors would remove a very powerful economic driving force from electronics development: Moore's Law https://www.cs.utexas.edu/~fussell/courses/cs352h/papers/moore.pdf

Gordon Moore was a physical chemist who was working as a process engineer. His paper pointed out that it was possible to "build" transistors on a wafer that were half as wide. This translates into four times as many transistors in a square area. He also said that this kind of process improvement could be repeated with a doubling every two years. He later amended this to 36 months. But the fact remains that there has never been any previous endeavor in human history where there was an equivalent 50 year stretch of performance improvement. There is no possible way that physical effects like vacuum tubes could deliver the lowered costs and improved performance that cooking from the quantum mechanical solid state physics cookbook did. So likely, we would still be in many respects, about as technically saavy as we were at the close of the Korean War. And doubtless no internet, as there would not have been the developments that made DARPA net transition to ARPA net and then the internet without solid state.

  • 2
    $\begingroup$ Moore's law is an observation, not a law per se. There's nothing saying that we are able to do miniaturization of electronics by some degree every some time period, except that we've been able to do so in the past. Sooner or later, if nothing else, you start hitting hard natural limits; for example, transistors can be made small, but not arbitrarily small. Waste heat needs to be transported away somehow. Etc. It's possible that some alternative technology may be found, but absent that, sooner or later we will hit a hard wall for how small electronics can get. $\endgroup$
    – user
    Commented Nov 6, 2017 at 10:02
  • $\begingroup$ @MichaelKjörling actually we did start hitting natural limits already. It is not heat. We are able to deal with some more heat. What we can't deal with, are actually quantum side-effects of such small transistors. Related: What limits CPU speed? and How small can CPUs get? (outside Stack Exchange) $\endgroup$
    – Mołot
    Commented Nov 6, 2017 at 16:35
  • 1
    $\begingroup$ Indeed, @Mołot. My mention of waste heat wasn't meant to build on the mention of size, but rather be a separate point; sorry if that wasn't clear. (To my defense, I was running out of space in the margin.) There's a reason why we've basically stopped clocking CPUs faster and are now instead focusing on things like faster memory access (including large on-die caches with clever cache algorithms), multiple cores, more clever execution pipelining tricks (of which things like predictive branching were only early steps), and so on and so forth. $\endgroup$
    – user
    Commented Nov 6, 2017 at 20:40

The phone system would have stayed analogue and no communication satellites would exist, so intercontinental communication would be limited to cables. So instead of millions of transatlantic "phone lines" you would be stuck at thousands. Say goodbye to globalisation.

Forget about modems, so there's no way to get computers to communicate over distance.

Since without small computers ballistic missiles would be not very precise (think V-2), you would probably have no ballistic missile submarines (they need a very good position fix to be somehow precise and forget about inertial navigation system using tubes) and few city-killer ballistic rockets, so your primary delivery system for nuclear weapons would be planes (B-52 without the better avionics). Also you have no good early warning systems (no satellites and no SAGE computer, although you could probably get a better Whirlwind).

This probably gives you a quite different cold war.

  • $\begingroup$ you can do sats with valves $\endgroup$
    – Jorge Aldo
    Commented Apr 13, 2015 at 22:45
  • 1
    $\begingroup$ en.wikipedia.org/wiki/Proximity_fuze you can even put radars into shells $\endgroup$
    – Jorge Aldo
    Commented Apr 13, 2015 at 22:47
  • $\begingroup$ you can do modems with vacuum tubes. $\endgroup$
    – Jorge Aldo
    Commented Apr 13, 2015 at 22:48
  • 1
    $\begingroup$ you can do precision missile guidance with vacuum tubes $\endgroup$
    – Jorge Aldo
    Commented Apr 13, 2015 at 22:53
  • $\begingroup$ None of htese are impossible. Just difficult. Likely expensive. $\endgroup$ Commented Nov 6, 2017 at 17:58

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