In terms of band theory , what is the difference between a conductor and a semi-conductor ?

Explanation

`to` In case of metals (conductors) the atomic orbitals forms molecular orbitals which are close in energy to each other as to form a band called valency band . If this band is partially filled (or) it overlaps with a higher energy unoccupied band called conduction band . Then electrons can flow easily under an applied electric field and the metal shows conductivity .
`to` In case of semi conductors , the gap between the valence band and conduction band is small . So some of electrons may jump to conduction band and show some conductivity .