How does a semiconductor’s band gap affect its ability to conduct electricity?

A semiconductor’s ability to conduct electricity is fundamentally determined by the size of its band gap, which is the energy range between the valence band (where electrons are normally bound) and the conduction band (where electrons move freely).12

Unlike metals, which have no band gap, or insulators, which have very wide band gaps, semiconductors possess a relatively narrow band gap. This narrow gap makes it possible for electrons to be excited from the valence band into the conduction band through thermal energy.12

When these electrons gain enough energy to cross the gap, they become free to participate in electrical conduction. Simultaneously, the movement of these electrons leaves behind vacancies known as holes, which act as positive charge carriers. The resulting electrical conductivity is intermediate—lower than that of metals but significantly higher than that of insulators. Because this gap is narrow, engineers can also manipulate a semiconductor's conductivity through doping or by tuning the band gap to create specialized electronic components like transistors and solar cells.12