In physics, some particles (for example electrons) follow the Pauli exclusion principle – i.e. that no two particles may occupy the same state at the same time. When a number of electrons are put into a system, electrons will occupy higher energy levels when the lower ones are filled up. Loosely speaking, the Fermi energy is the energy of the highest occupied state at zero temperature. It is given the symbol EF. Fermi energy is a concept which finds application in semiconductor theory and device design.
Fermi energy was named after Enrico Fermi, who with Paul Dirac, derived the Fermi-Dirac statistics. These statistics allow one to predict the behaviour of large numbers of electrons under certain circumstances, especially in solids. The equations of quantum mechanics would otherwise be too hard to solve in such situations.