Extrinsic semiconductor a term used for those semicondutors in which certain impurities are added to increase their conductivity over the pure form. These impurities are called dopants. These impurities either donate extra conduction electrons to the semiconductor or create holes by accepting valence electrons from the material, thereby increasing the conductivity of the material.
Intrinsic semiconductors, on the other hand, are without any dopants, and the conduction is due to any free electrons or holes present in the material. These are produced by thermal excitations of valence band electrons into the conduction band. The number of electrons and holes is nearly equal. Conductivity of intrinsic semiconductors is much less than that of extrinsic semiconductors.