1. A substance that can act as an electrical conductor or insulator depending on chemical alterations or external conditions. Examples are silicon, germanium, and gallium arsenide.
Also called "III-V" materials since semiconductor elements are in groups III and V of the periodic table of chemical elements.
2. An electronic device (e.g. a transistor, diode, or integrated circuit) manufactured from semiconductor materials.
Semiconductor devices control and amplify because a small voltage or current, or a physical stimulus (such as light or pressure), allows the semiconductor to pass or block electrical current. Devices can be fabricated with other capabilities such as passing electric current in only one direction, emitting light, mixing and transforming signals, etc.