1. A semiconductor material has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Their resistance decreases as their temperature increases, which is behavior opposite to that of a metal. Their conducting properties may be altered in useful ways by the deliberate, controlled introduction of impurities ("doping") into the crystal structure. Where two differently-doped regions exist in the same crystal, a semiconductor junction is created. The behavior of charge carriers which include electrons, ions and electron holes at these junctions is the basis of diodes, transistors and all modern electronics.
2. Any of various solid substances, such as silicon or germanium, that conduct electricity more easily than insulators but less easily than conductors. Semiconductors are able to do this because they have a small number of electrons that have escaped from the bonds between the atoms, leaving open spaces. Both the electrons and the open spaces can carry an electric current.
https://en.wikipedia.org/wiki/Semiconductor (1.); http://www.thefreedictionary.com/semiconductor (2.)
Author: Svenja Gutt