electronic device in which electricity flows through solid semiconductor crystals ( silicon, gallium arsenide, germanium) rather than through vacuum tubes. The first solid-state device was the “cat's whisker” (1906), in which a fine wire was moved across a solid crystal to detect a radio signal. Transistors (transistor), made of one or more semiconductors, are at the heart of modern solid-state devices; in the case of integrated circuits (integrated circuit), millions of transistors can be involved. See also electronics.