2DEG in inversion and accumulation layers on narrow-gap and gapless ( epsilon g<or=0) Hg1-xCdxTe were investigated by using capacitance spectroscopy in magnetic fields Although 2D states in investigated systems with epsilon g<or=0 are supposed to be resonant states, capacitance magneto-oscillations are distinctly resolved. Broadening of Landau levels does not differ significantly from that in HgCdTe with epsilon g>0. The experimental subband parameters are in a very good agreement with theoretical calculations, which ignore the interband tunnelling. The stationary character of 2D states in Kane semiconductors may be understood in the framework of the conception developed for the description of the vacuum condensate of electrons near nuclei with supercritical charge. Even for epsilon g=0 the effective quasi-relativistic potential provides a non-penetrating or a slightly penetrating barrier for 2D states. As a result more than 97% of subband states are true stationary states or are well defined. If the author takes into account the spin polarization terms in the effective potential, all the states turn out to be true stationary states.