Question: What technology supplanted vacuum tubes?
About the article "Electron", section "Other applications".

Candidate passages:
Vacuum is space that is devoid of matter.
The word stems from the Latin adjective "vacuus" for "vacant" or "void".
An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure.
Physicists often discuss ideal test results that would occur in a "perfect" vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space.
The Latin term in vacuo is used to describe an object as being in what would otherwise be a vacuum.
The "quality" of a partial vacuum refers to how closely it approaches a perfect vacuum.
Other things equal, lower gas pressure means higher-quality vacuum.
For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%.
Much higher-quality vacuums are possible.
Ultra-high vacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth (10−12) of atmospheric pressure (100 nPa), and can reach around 100 particles/cm3.
Outer space is an even higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average.
According to modern understanding, even if all matter could be removed from a volume, it would still not be "empty" due to vacuum fluctuations, dark energy, transiting gamma- and cosmic rays, neutrinos, along with other phenomena in quantum physics.
In modern particle physics, the vacuum state is considered as the ground state of matter.
Vacuum has been a frequent topic of philosophical debate since ancient Greek times, but was not studied empirically until the 17th century.
Evangelista Torricelli produced the first laboratory vacuum in 1643, and other experimental techniques were developed as a result of his theories of atmospheric pressure.
A torricellian vacuum is created by filling with mercury a tall glass container closed at one end and then inverting the container into a bowl to contain the mercury.
Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, and a wide array of vacuum technology has since become available.
The recent development of human spaceflight has raised interest in the impact of vacuum on human health, and on life forms in general. 
In the free-electron laser (FEL), a relativistic electron beam passes through a pair of undulators that contain arrays of dipole magnets whose fields point in alternating directions.
The electrons emit synchrotron radiation that coherently interacts with the same electrons to strongly amplify the radiation field at the resonance frequency.
FEL can emit a coherent high-brilliance electromagnetic radiation with a wide range of frequencies, from microwaves to soft X-rays.
These devices may find manufacturing, communication and various medical applications, such as soft tissue surgery.
Electrons are important in cathode ray tubes, which have been extensively used as display devices in laboratory instruments, computer monitors and television sets.
In a photomultiplier tube, every photon striking the photocathode initiates an avalanche of electrons that produces a detectable current pulse.
Vacuum tubes use the flow of electrons to manipulate electrical signals, and they played a critical role in the development of electronics technology.
However, they have been largely supplanted by solid-state devices such as the transistor.
The quality of a vacuum is indicated by the amount of matter remaining in the system, so that a high quality vacuum is one with very little matter left in it.
Vacuum is primarily measured by its absolute pressure, but a complete characterization requires further parameters, such as temperature and chemical composition.
One of the most important parameters is the mean free path (MFP) of residual gases, which indicates the average distance that molecules will travel between collisions with each other.
As the gas density decreases, the MFP increases, and when the MFP is longer than the chamber, pump, spacecraft, or other objects present, the continuum assumptions of fluid mechanics do not apply.
This vacuum state is called "high vacuum", and the study of fluid flows in this regime is called particle gas dynamics.
The MFP of air at atmospheric pressure is very short, 70 nm, but at 100 mPa (~1×10−3 Torr) the MFP of room temperature air is roughly 100 mm, which is on the order of everyday objects such as vacuum tubes.
The Crookes radiometer turns when the MFP is larger than the size of the vanes.
Vacuum quality is subdivided into ranges according to the technology required to achieve it or measure it.
These ranges do not have universally agreed definitions, but a typical distribution is shown in the following table.
As we travel into orbit, outer space and ultimately intergalactic space, the pressure varies by several orders of magnitude.
Atmospheric pressure is variable but standardized at 101.325 kPa (760 Torr).
Low vacuum, also called "rough vacuum" or "coarse vacuum", is vacuum that can be achieved or measured with rudimentary equipment such as a vacuum cleaner and a liquid column manometer.
Medium vacuum is vacuum that can be achieved with a single pump, but the pressure is too low to measure with a liquid or mechanical manometer.
It can be measured with a McLeod gauge, thermal gauge or a capacitive gauge.
High vacuum is vacuum where the MFP of residual gases is longer than the size of the chamber or of the object under test.
High vacuum usually requires multi-stage pumping and ion gauge measurement.
Some texts differentiate between high vacuum and "very high vacuum."
Ultra high vacuum requires baking the chamber to remove trace gases, and other special procedures.
British and German standards define ultra high vacuum as pressures below 10−6 Pa (10−8 Torr).
Deep space is generally much more empty than any artificial vacuum.
It may or may not meet the definition of high vacuum above, depending on what region of space and astronomical bodies are being considered.
For example, the MFP of interplanetary space is smaller than the size of the solar system, but larger than small planets and moons.
As a result, solar winds exhibit continuum flow on the scale of the solar system, but must be considered as a bombardment of particles with respect to the Earth and Moon.
Perfect vacuum is an ideal state of no particles at all.
It cannot be achieved in a laboratory, although there may be small volumes which, for a brief moment, happen to have no particles of matter in them.
Even if all particles of matter were removed, there would still be photons and gravitons, as well as dark energy, virtual particles, and other aspects of the quantum vacuum.
Hard vacuum and soft vacuum are terms that are defined with a dividing line defined differently by different sources, such as 1 Torr, or 0.1 Torr, the common denominator being that a hard vacuum is a higher vacuum than a soft one.  
This LINK will show you what a 1915 Advertisement by Audio Tron Sales looked like.
The flyer explains the advantages over competitor vacuum tubes and gives testimonials from users. 
Amperex Electronic Corporation was a manufacturer of vacuum tubes and semiconductors.