The Fermi level ($E_F$) represents the energy state at which the probability of occupancy by an electron is exactly $0.5$.

• In an intrinsic semiconductor, the concentration of electrons in the conduction band ($n$) equals the concentration of holes in the valence band ($p$).
• This symmetry forces $E_F$ to lie almost exactly in the middle of the forbidden energy gap ($E_g/2$).
• In n-type, $E_F$ shifts towards the conduction band; in p-type, it shifts towards the valence band.