费米能阶（英语：Fermi level），通常标示为「µ 」或「E_F」。

-e为基本电荷。

费米迪拉克分布可由下式表述：

其结果如右图所示，f越接近1，表示该能量被电子占据的概率越大，f越接近于0，表示该能量被电子占据的概率越小。如图所示，费米能级为0.55eV, 费米能级之上越高，f越接近于0；费米能级之下，能量越低，f越接近于0。

The Fermi level is the total chemical potential for electrons (or electrochemical potential for electrons) and is usually denoted by µ or E_F. The Fermi level of a body is a thermodynamic quantity, and its significance is the thermodynamic work required to add one electron to the body (not counting the work required to remove the electron from wherever it came from). A precise understanding of the Fermi level—how it relates to electronic band structure in determining electronic properties, how it relates to the voltage and flow of charge in an electronic circuit—is essential to an understanding of solid-state physics.