An oxidized layer was obtained on a cadmium zinc telluride (CZT) wafer by using chemical etching first in a KOH-KCl solution and then in an NH4F/H2O2 solution. The oxidized layer on the CZT obtained by using this method was analyzed by using ex-situ spectroscopic ellipsometry (SE) for the first time. In particular, the optical constants and the thickness of the chemical oxidized layer were obtained as functions of the oxidizing time.