This paper presents a new simple method of HgCdTe surface treatment which consists of chemical oxidation of HgCdTe with nitric acid and removal of the oxide with ammonium hydroxide, The electrical properties of the electron-beam deposition CdTe passivation of Hg0.7Cd0.3Te are investigated with regard to the effects of HgCdTe surface etching, exposure to nitric acid, and the new surface treatment method. As the HgCdTe surface is progressively etched with bromine in methanol (Br-MeOH), the surface becomes rougher and a higher density of fixed charge is induced at the interface between CdTe and HgCdTe. Exposure to HNO3 results in a very high density of fixed charge and performance degradation in metal insulator semiconductor (MIS) capacitors, which is due-to the chemical oxide grown by HNO3. The oxide growth rate is enhanced as the concentration of HNO3 increases or as more H2O is added. This oxide can be removed with NH4OH. After the new surface treatment, MIS capacitors of Hg0.7Cd0.3 Te show substantial improvement in electrical properties, such as low density of fixed charge and reduced hysteresis width, regardless of previous surface etching.