Why pure semiconductor just behave like an insulator?

At absolute zero (0K), an intrinsic semiconductor will act like a perfect insulator. At this temperature, the electrons in the valence band will remain there. The heat energy required to excite the electrons from the valence band to the conduction band is insufficient at 0K. When the temperature increases, some of the electrons from the valence band got excited and moves to the conduction band. This will give rise to the conductivity of the semiconductor.

i.e

in 0 k(0 kelvin) the pure semi conductor the electrons in the valance band don't do any thing.They are lazy for conductivity.But when increasing the temperature increase the energy of electrons and they try to move.At the end electrons win and they can to move.So it happened a conductivity.