What is semiconductor ?

The materials, whose electrical properties lie between those of conductors and insulators, are know as semiconductor.
The exampels of such materials are-
»cadmium sulphides(CdS),
«gremanium(Ge),
»silicon(Si),
«gallium arsenide(GaAs),
»lead telluride  etc

In terms of energy bands , the semiconductors may be defined as those materials, which at room temperature, have

(i) Partial filled conduction band
(ii)Partial filled valenced band

In semiconductor, at absolute zero temperature there are no electrons in the conduction band and the valence band is completely filled. Thus semiconductors behaves like perfect insulators at 0°K.
However, as the temperature increased, the width of energy gap reduces. Consequently, some of the electrons jump into conduction band and semiconductor show some conductivity. It is thus obvious, that the conductivity of semiconductor increase in temprature.