Vacuum Tubes.

Before transistors, electronic equipment consisted of glass tubes containing electronic components. The inside of the tubes was kept in a vacuum to avoid air interference with their function. The concept of replacing these tubes with simpler devices started in the late 1930s at Bell Labs, the research arm of the old national AT&T telecommunications monopoly. The idea was shelved during World War II.

Germanium.

Using semiconductor materials made out of the metal germanium, a crude device was developed in late 1947. William Shockley, John Bardeen, and Walter Brattain are credited with developing the transistor, but they worked with a large number of people at Bell Labs in the process. There were two problems with the original transistor. One was obtaining enough germanium to produce meaningful quantities of transistors. The other was purifying germanium adequately. Gordon Teal and J. B. Little at Bell...