The comparative study of the spin splitting of two-dimensional subbands in surface layers on small gap (Formula presented)(Formula presented)Te, with direct ((Formula presented)≳0) and inverted ((Formula presented)<0) bands, is carried out experimentally and theoretically. The occupations of spin-splitted subbands (Formula presented) are determined from Fourier transforms of capacitance magneto-oscillations of (Formula presented)(Formula presented)Te metal-oxide-semiconductor structures. The values ((Formula presented)-(Formula presented))/((Formula presented)+(Formula presented)) are found to be independent of surface densities (Formula presented), subband index i, and |(Formula presented)| at high enough (Formula presented) when the band bending sufficiently exceeds the gap (Formula presented) and the conditions corresponding to pseudoultrarelativistic behavior of surface electrons are fulfilled. However, they are different for (Formula presented)≳0 and (Formula presented)<0 cases. To analyze spinlike effects in narrow-gap and gapless semiconductors, we employed for Kane Hamiltonian the conception, offered by Zel’dovich and Migdal for the description of vacuum condensate of Dirac’s electrons near supercritical nuclei. In this way, we obtain “usual” Schrodinger-like subband equations with some effective potential. The terms responsible for nonparabolicity, spin-orbit splitting, and “resonant” shift, due to interband mixing by surface electric fields, are easily singled out. Such equations admit the simple physical interpretation, and difference in values of “spin” effects for (Formula presented)≳0 and (Formula presented)<0 cases is easily seen. The dependencies of total subband occupations (Formula presented)=(Formula presented)+(Formula presented) and average cyclotron masses on (Formula presented) nevertheless are close for both cases in agreement with previous experimental observations. In a pseudoultrarelativistic limit (Formula presented)=0 the simple analytical expressions for subband parameters of experimental interest are obtained with an allowance for spin effects. The calculations agree with experiment for (Formula presented)(Formula presented)Te with both direct and inverted bands, excluding the region of low (Formula presented) in heavily doped samples. Possible reasons for disagreement are discussed.