How do semiconductors differ from electrical conductors and insulators?

Materials are classified into conductors, insulators, and semiconductors based on their band structure, specifically the presence and size of a band gap—a range of energy levels that electrons cannot occupy.12

Key Differences in Conductivity

• Conductors (Metals): These materials lack a band gap at the Fermi level, meaning the valence band and conduction band overlap or are continuous. Consequently, electrons move freely, making metals excellent conductors.123
• Insulators: These possess very wide band gaps that prevent electrons from reaching the conduction band under normal conditions. This results in extremely low electrical conductivity.124
• Semiconductors: These have relatively narrow band gaps. While they act as insulators at absolute zero, their narrow gaps allow electrons to be thermally excited into the conduction band at higher temperatures, resulting in intermediate conductivity.1253

Unlike conductors, where conductivity decreases with rising temperature due to thermal agitation, the conductivity of semiconductors increases with temperature and can be further enhanced through doping—the intentional addition of impurities to create free charge carriers.543