Capacitance−voltage characteristics of metal dielectric semiconductor structures with atomic layer deposition Al2O3 on n- and p-Cd0.22Hg0.78Te (with and without a surface graded-gap layer) preliminary oxidized in oxygen glow discharge plasma (with the resulting oxide thickness of 2 nm) have been studied. The obtained structures reveal the positive fixed charge with a density of ∼ (1−6) · 10^11 cm^(−2). The ratio between a slow surface states density and a surface band gap width is almost independent on graded-gap layer presence, with the value of ∼ (4−8) · 10^11 cm^(−2) · eV^(−1). The proposed passivation approach provides near-ideal low-frequency capacitance-voltages characterized by weak influence of fast surface states. Films of CdHgTe grown without the graded-gap surface layer are proved to be much more sensitive to the process of oxidation in glow discharge plasma.