The invention of the transistor in 1947 by John Bardeen, Walter H. Brattain, and William B. Shockley of the Bell research staff provided the first of a series of new devices with remarkable potential for expanding the utility of electronic equipment (see photograph). Transistors, along with such subsequent developments as integrated circuits, are made of crystalline solid materials called semiconductors, which have electrical properties that can be varied over an extremely wide range by the addition of minuscule quantities of other elements. The electric current in semiconductors is carried by electrons, which have a negative charge, and also by “holes,” ...(100 of 8970 words)