that of an insulator but much smaller than that of a metal.At low
temperatures the valence band remains full ,the conduction band is
empty and these materials are insulators at low temperatures.The
conductivity of these materials increases with increase in temperature
and hence these are called as intrinsic semiconductors.As the
temperature is increased some me the electrons in the valence band
acquire thermal energy greater than the energy gap and move to
conduction band.Therefore now these electrons are free to move about
under the influence of even a small applied field.These electrons are
called as conduction electrons.The practically used semiconductors are
germanium and silicon. 18:49
