Why do metals conduct electricity better than semiconductors according to band theory?

According to band theory, the difference in electrical conductivity between metals and semiconductors is primarily determined by the presence or absence of a band gap—a range of forbidden energy levels between the valence band and the conduction band.12

• Metals: Metals are excellent conductors because they lack a band gap at the Fermi level. The valence band and conduction band overlap or are continuous, meaning there is no forbidden energy barrier for electrons to overcome. Consequently, a fraction of electrons is always present in the conduction band, allowing them to move freely and conduct electricity with ease.12
• Semiconductors: Semiconductors possess a relatively narrow band gap. At low temperatures, electrons are bound in the valence band and cannot conduct electricity. For conduction to occur, electrons must gain enough energy—typically through thermal excitation—to cross the forbidden gap into the conduction band. Because this requires overcoming an energy barrier, semiconductors are significantly less conductive than metals.1342