Results of researches concerning the properties of the two-dimensional (2D) degenerate electron gas in a single quantum well on the basis of the InAs/AlSb heterostructure are reported. The non-parabolic character of the InAs and AlSb conduction bands is described by a simplified Kane model. The dispersion curves for first three subbands are calculated, as well as the dependences of the Fermi energy, subband filling, and effective mass of electrons at the Fermi level on the total 2D electron concentration. The obtained results are in good agreement with experimental data.