Draw separate energy band diagrams for conductors, semi-conductors and insulators and label each of them.
Energy band diagrams for conductor, semiconductor and insulator are shown above.
In conductors, both the valance band and conduction band overlap each other. So there is zero band gap in a conductor.
In semiconductor, there is a small band gap approximately of 1 eV.
In an insulator, there is a large band gap of nearly 5 eV.