1. Conductor (Metal)
In conductor the conduction band and valence band overlap each other.
Electron can easily jumped to conduction band and available for conduction of electricity.
2. Insulator
In insulator, The Valence band is completely filled and conduction band is completely empty and the energy gap is large.
3. Semiconductor
In semiconductor, The valence band is totally filled and the conduction band is empty but the energy gap between valeance band and conduction band is very small. So at very small temperature electron can jump from valence band to conduction band.
Also Read: CBSE Class 12 Physics Chapter-14 (Semiconductor and Electronic Devices) All Topics