Why is crystalline boron a semiconductor?

Pure crystalline boron is classified as a semiconductor because its electrical conductivity is temperature-dependent: it acts as an insulator at low temperatures and conducts electricity like a metal at high temperatures.1

In a semiconductor, atoms are arranged in a periodic crystal structure where electrons occupy specific energy bands. At low temperatures, electrons are bound within the valence band, preventing electrical conduction. As the temperature increases, thermal energy allows some electrons to overcome the energy gap (bandgap) and move into the conduction band, where they become free to participate in current conduction.2

Crystalline boron's unique electronic behavior is a result of this band structure, which is characteristic of semiconductor materials. While boron is often used as a doping agent to modify the conductivity of other semiconductors like silicon, its own pure crystalline form exhibits these intrinsic semiconducting properties.21