Why does the electrical conductivity of many semiconductors increase as temperature rises?

In materials science, the electrical conductivity of semiconductors increases with temperature primarily because of the nature of their energy bands.

At low temperatures, electrons in a semiconductor are bound within the valence band and are not available for conduction. These electrons are separated from the conduction band by a narrow energy gap, or bandgap, which they cannot normally cross.12

As temperature rises, thermal energy allows an increasing number of electrons to break their covalent bonds and gain enough energy to jump across the bandgap into the conduction band. This process creates two types of charge carriers:12
* Free electrons: The electrons that have moved into the conduction band.12
* Holes: The positively charged vacancies left behind in the valence band.12

When an electric field is applied, both these free electrons and holes move through the crystal, resulting in an increase in electrical conductivity. While the mobility of these carriers may decrease at higher temperatures, the significant rise in the total number of available charge carriers dominates, leading to a net increase in conductivity.12