能隙（band gap或energy gap）也译作能带隙（energy band gap）、禁带宽度（width of forbidden band），在固态物理学中泛指半导体或是绝缘体的价带顶端至传导带底端的能量差距。

对一个zh-cn:本征半导体而言，其导电性与能隙的大小有关，只有获得足够能量的电子才能从价带被激发，跨过能隙并跃迁至传导带。利用费米-狄拉克统计可以得到电子占据某个能阶的机率。又假设，是所谓的费米能阶，电子占据的机率可以利用波兹曼近似简化为：

In solid-state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It is closely related to the HOMO/LUMO gap in chemistry. If the valence band is completely full and the conduction band is completely empty, then electrons cannot move in the solid; however, if some electrons transfer from the valence to the conduction band, then current can flow (see carrier generation and recombination). Therefore, the band gap is a major factor determining the electrical conductivity of a solid. Substances with large band gaps are generally insulators, those with smaller band gaps are semiconductors, while conductors either have very small band gaps or none, because the valence and conduction bands overlap.