The vacuum tube was replaced with what electrical component?

The vacuum tube was replaced with transistor.

Explanation:

The invention of semiconductor was very useful in making solid state transistor that allowed the production of small yet faster, cheaper, and more trusted and reliable computers. These solid state transistor is so often used that, it nearly replaced all the use of transistor. This replacement took place after the invention of semiconductor in the year around 1940. Vacuum tubes also known as thermionic tubes are not used anymore in computers and electronics.