As we know that the forbidden energy gap in case of semiconductors is very small. At the temperature of zero Kelvin no electron will leave the valence band. So, conduction band will remain empty at zero Kelvin.
But at room temperature the energy gap of 1eV is covered by some of the electrons. These electrons gain some thermal energy and jump from the valence band to conduction band. When these electrons jump from valence to conduction band then as a result some empty spaces are created in the valence band. This empty vacancy or space is known as hole. A Hole can be considered as the space for any positive charge of equivalent amount as that of the electron. Hole is also an active entity of the valence band. As we know the conductivity in the conduction band is due to the presence of the free electrons. Similarly, these holes also play some role in increasing the conductivity of the semi conductor to some extent. These holes also show some movement in valence band. This movement of holes also increases the overall conductivity of the semi conductors.