Question

according to band theory compare a semiconductor with a insulator

Answer 1

According to band theory
Semiconductor at 0K valence band is filled and conductionband is empty. At room temperature conductionband is partially filled and valence band is partially filled. At high temperature it acts as conductor
In insulator the energy gap is greater than 3eV. Valence band is completely filled and conduction band is empty . So no current conduction takes place