半金属（英语：semimetal）是指导带和价带之间相隔很窄的材料。根据能带理论，固体根据这个间隔从宽到窄，可以依次分为金属、半金属、半导体和绝缘体。对于半导体和绝缘体，导带和价带之间的间隔相对较大，使得费米能级附近电子的态密度等于零，成为带隙。其中绝缘体的带隙比半导体的大，但具体的分界线比较模糊。而对于半金属，导带和价带之间的间隔十分小，使得费米能级附近电子的态密度接近于零但不为零，因此也没有带隙。金属的费米能级则在导带当中，附近有足够大的电子态密度，使得电流可以良好地传导。

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.