is Fermi level is valid for other than metals?

Answer 1

All fermions have associated with them Fermi energies, or Fermi levels, so the answer is yes. it is the smallest energy step from the ground state of any fermion, which includes not only all the atoms, but all particles with half integral spins, like electrons.

Correction: Some pairs of fermions form bosons, which have whole integer spins, such as Cooper pairs, two electrons in a bound state which can happen under certain circumstances. Then the Fermi level doesn't apply, and Bose-Einstein statistics take over.

Answer 2

All solids have a Fermi level. It is simply the highest electron energy level at absolute zero. The location of the Fermi level relative to the valence and conduction bands determines the electrical properties of the material.