A method of analyzing a nitride semiconductor layer in which a mixing ratio at a ternary mixed-crystal nitride semiconductor layer can be analyzed non-destructively, simply, and precisely, even its surface is covered with a cap layer is provided. The nitride semiconductor layer having an AN layer or a BN layer with a thickness of 0.5 to 10 nm that is stacked on an AxB1-xN layer (A and B: 13 group elements, 0≦x≦1) is subjected to reflection spectroscopy to obtain a reflection spectrum of the AxB1-xN layer. Let an energy value in a peak position of the reflection spectrum be a band gap energy Egap, and let a band gap energy value of AxB1-xN (x=1) be EA and a band gap energy value of AxB1-xN (x=0) be EB, x is calculated from Equation Egap=(1−x)EB+xEA−bx(1−x) (where b is bowing parameter corresponding to A and B).