transistor 
A device composed of semiconductor material that is used to amplify analog signals in radio and television communications or to open and close digital circuits in electronic devices such as computers and mobile phones. Invented in 1947 at Bell Labs, the transistor was hailed as a smaller, less-expensive, and cooler-running replacement for the vacuum tubes then commonly used to amplify current in electronic devices. Today, millions of transistors are packed into silicon chips to create computer processors.