The Fermi Level is the energy level of the valence electrons at 0 K. it is also the upper limit of the valence band. if the Fermi level is above the lower end of the conduction band (like metals), the valence electrons have enough energy to flow, and the material is thus a good conductor. If the Fermi level is separted from the lower end of the conduction band by a large gap, then the electrons do not have enough energy to escape their bonds (insulators). However, if this band gap is small (semi conductors), the electrons could be externally excited (eg., thermally, electric field) in order to jump into the conduction band and flow.
i read somewhere that fermi level is situated at the middle of energy band gap for intrinsic semiconductors,above the center for n-type semiconductors and below the center for p-type semiconductors.i,however,am not able to understand the reason behind it.please help.