Whereas polymers are highly visible engineering materials with a major impact on contemporary society, semiconductors are relatively invisible but have a comparable social impact. Technology has clearly revolutionized society, but solid-state electronics is revolutionizing technology itself. A relatively small group of elements and compounds has an important electrical property, semi-conduction , in which they are neither good electrical conductors nor good electrical insulators. Instead, their ability to conduct electricity is intermediate. These materials are called semiconductors , and in general, they do not fit into any of the four structural materials categories based on atomic bonding.
Metals are inherently good electrical conductors.
Taken from Introduction to Materials Science for Engineers , James F. Shackelford, Prentice Hall , Inc., New Jersey. It is perhaps best illustrated by the production of integrated circuit devices. An excellent montage representing IC processing is illustrated in the following IBM gif. The gray substrate under the pink, white, yellow and green metallization pattern, is the silicon wafer, which is a semiconductor material. The image to the left shows the first transistor, discovered by Bardeen, Brattain and Shockley at Bell Labs.