What is "semimetal"

Semimetal \Sem"i*met`al\, n. (Chem.) An element possessing metallic properties in an inferior degree and not malleable, as arsenic, antimony, bismuth, molybdenum, uranium, etc. [Obs.]

n. (context inorganic chemistry English) A metalloid.

A semimetal is a material with a very small overlap between the bottom of the conduction band and the top of the valence band. According to electronic band theory, solids can be classified as insulators, semiconductors, semimetals, or metals. In insulators and semiconductors the filled valence band is separated from an empty conduction band by a band gap. For insulators, the magnitude of the band gap is larger (e.g. > 4 eV) than that of a semiconductor (e.g. < 4 eV). Metals have a partially filled conduction band. A semimetal is a material with a very small overlap between the bottom of the conduction band and the top of the valence band. A semimetal thus has no band gap and a negligible density of states at the Fermi level. A metal, by contrast, has an appreciable density of states at the Fermi level because the conduction band is partially filled.