THE SEMICONDUCTOR in which number of electrons or holes is smaller than N_c and N_v density of state in CB or VB are called non-degenerate semiconductor. The general exponential expression for the concentration of electron in the conduction band (CB), is based on replacing Fermi-Dirac statistics with Boltzmann statistics, which is only valid when E_c is several KT above E_f. In other words we assumed that the number of states in the conduction band far exceed the number of electrons there N_c is the measure of the density of states in CB. The Boltzmann expression for n is valid only when n<c. Those semiconductors for which n<cand P<v are termed as Non -degenerate semiconductors. When the semiconductor has been excessively doped with donors, then n may be large typically 10¹⁹-10²⁰ cm^-3 or greater then N_c . Semiconductor that have n>>N_c or P>>N_v are called Degenerate semiconductor. In this case Pauli Exclusion Principle becomes important in the electron statistics and we use Fermi Dirac statistics. Degenerate semiconductor is used in laser diodes, Zener diodes and ohm contacts in ICs and as metal gates in many microelectronic MOS devices.