What does solid-state mean in relation to electronics?

Three common solid state components are displayed.
Three common solid state components are displayed. Clockwise from the top: inch-long circuit chip, red light-emitting diode and a transistor. 

Solid-state electronic devices are part of our everyday lives. The transistor, invented in 1947 by Bell Labs, was the first solid-state device to come into commercial use in the 1960s. Solid-state electronic devices have replaced vacuum tubes in just about all electronics devices. Vacuum tubes are still used in the transmitters of radio stations you listen to, many guitar amplifiers and some audiophile equipment. Vacuum tubes are the opposite of "solid-state" because tubes burnout, break, etc.

One of the first solid-state devices was a crystal radio. In a crystal radio, a piece of wire positioned on a crystal's surface is able to separate the lower-frequency audio from the higher-frequency transmitted radio carrier wave. This form of signal detection is due to the crystal's ability to pass a current in only one direction. For more details, see How Radio Works.


Solid-state gets its name from the path that electrical signals take through solid pieces of semi-conductor material. Prior to the use of solid-state devices, such as the common transistor, electricity passed through the various elements inside of a heated vacuum tube. Solid-state devices, such as a transistor, use conductors to control the flow of signals through a circuit.

  • In a transistor amplifier, a small change on the input signal's amplitude is immediately reflected in larger amplitude in the output within a transistor.
  • In a vacuum tube amplifier, after the tube warms up, a signal is applied to the "grid" of a tube and the resultant output of the same frequency is at a much higher amplitude.

In the sandwich-like construction of a transistor, the emitter, base, and collector do a similar task at much lower DC voltages, with no "warm-up" time! In digital circuits, an integrated circuit chip is nothing more that a collection of transistors and wires that hook them together.

­ Solid state devices called diodes have a replaced rectifier vacuum tubes, used to transform alternating current (AC) to direct current (DC). Cool-running light-emitting diodes (LEDs), another solid-state device used for indicators on the front panel of your computer and monitor, have replaced the earlier incandescent bulbs. Multiple bright LEDs are also used for the third stoplight on many U.S. vehicles and for traffic signals.

Solid-state miniature electronic components are in many places:

  • Mounted on flexible thin film printed circuits in cameras and disk drives.
  • The beeping sound made by a cell phone, page or auto dashboard alarm.
  • The voice chip in an answering machine.
  • TV remote control.
  • Laser pointer.
  • The inside of an MP3 player.
  • A quartz watch.
  • The image sensor in a digital camera and a camcorder.
  • The computer monitor you are viewing.
  • The mouse you will click to the next HSW screen!

See the links that follow for more information about solid-state electronics.