The complex dielectric function, &egr;(E)=&egr;1(E)+i&egr;2(E), of hexagonal CdSe has been measured by spectroscopic ellipsometry in the photon‐energy range between 1.2 and 5.3 eV at room temperature. The measured spectroscopic‐ellipsometry data are analyzed on the basis of a simplified model of the interband transitions. The model is based on the Kramers–Kronig transformation and includes theE0(E0&agr; ; &agr;=A,B,C),E1(E1&agr; ; &agr;=A,B,C), andE0′gaps as the main dispersion mechanisms. The recent SE data of cubic, zinc‐blende‐type CdSe have also been analyzed with the same model by considering the critical points for the cubic phase (i.e.,E0,E0+&Dgr;0,E1,E1+&Dgr;1, andE2). Results are in satisfactory agreement with the experimental data over the entire range of photon energies. To facilitate design of various optoelectronic devices, dielectric‐function‐related optical constants, such as the complex refractive index, absorption coefficient, and normal‐incidence reflectivity, of these crystals are also presented. ©1995 American Institute of Physics.