The conductivity of semiconductor can be increased by the following methods:
1. By doping: The addition of impurity atoms to a pure-semi-conductor is known as doping. The doping is done to increase the conductivity of a pure semi-conductor. It must be noted that the impurity atom is about 1 in every 1010 atoms.
2. By increase in temperature: In case of a Semi-Conductor there is an energy gap between the valence band and the conduction band but at OK no electron has sufficient energy to cover this gap. So, when temperature of Semi-Conductor is increased, covalent bands may break up and some of the electrons may acquire sufficient energy to cover this gap thereby increasing the conductivity. Whereas in case of metals, with the increase in temperature the collisions increase due to which there is more hindrance to the flow of electrons which will ultimately decrease the conductivity.