The effect of combined gas-phase introduction of vanadium(V) and manganese(IV) oxides on thermal oxidation of InP consists in acceleration of the oxide film formation on the InP samples regardless of the chemostimulators mixture composition. The nonlinear oxide film thickness at the InP surface as a function of the chemostimulators mixture composition has been rationalized as a result of mutual influence of V 2 O 5 and MnO 2 changing their heat-induced reactivity and evaporation behavior. Keywords: indium phosphide, vanadium(V) oxide, manganese(IV) oxide, thermal oxidation, ellipsometry Studies of combined influence of chemostimulator oxides on thermal oxidation of GaAs [1] including that induced by vanadium(V) and manganese(IV) oxides [2] have shown nonlinear change in the oxide film thickness at the sample surface as a function of the stimulators mixture composition. Magnetron deposition of the chemostimulators (the catalyst oxide V 2 O 5 + the transistor oxide PbO) mixture onto the InP surface has revealed the change of catalytic mechanism of the semiconductor oxidation to the transit one; the nonlinear effect of the combined action of the chemostimulators can be used for fine tuning of the composition and properties of the films [3].We report here on the oxidation of indium phosphide induced with variable-composition mixtures of V 2 O 5 and MnO 2 introduced via the gas phase. Fig. 1 displays a representative spectrum of ellipsometry parameters ψ and ∆ for the oxide film obtained at the thus treated InP surface.The spectra interpretation was performed applying several methods; generally, the single-layer model was used. The optical constants of the film were specified proceeding from the expected properties; for instance, the Cauchy equation n = n 0 + A/λ 2 [4, 5] well described refractive index of dielectrics, whereas the Bruggeman model [5,6] treated the film as a dielectric matrix with metal inclusions. Then the experimental data were fitted with those equations in order to estimate the fitting parameters n 0 and А, the film thickness d, and the fitting quality.As described above, the processing of spectral ellipsometry yielded thickness d of the oxide film formed at the InP surface upon thermal oxidation in the presence of V 2 O 5 and MnO 2 as a function of the chemostimulators mixture composition (Fig. 2).