Materials having resistivity or conductivity in between conductors and insulators, are called semiconductors. These are the materials with the forbidden energy gap between valence and conduction band <3eV. It is less than that of insulators (>3eV) and more than that of conductors.
Elemental semiconductor: Germanium, silicon, selenium, etc. Compound semiconductors: Gallium, arsenide, Indium, phosphide, cadmium, sulphide etc.
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