The Fermi distribution function:

where, E is the electron energy, Ef is the Fermi energy, and T is the absolute temperature. Its physical meaning is that:

As can be seen from the formula, the probability of occupancy for an arbitrary energy state at E depends on the value of Fermi energy Ef, and on the value of temperature T.

The effects of Ef and T on this probability distribution function can be seen from the following applet.