The density of states (DOS) of two-dimensional (2D) electrons in perpendicular magnetic fields was reliably extracted from the magneto-capacitive response of double-barrier structures. The model calculations with a Gaussian-like DOS were compared with the experimental C vs. B curves, measured at different biases and temperatures. The results show that the fittings are remarkably good, and the Landau level model DOS is obtained. Unlike the cdnventionally used heterostructure method, the new measurements have no in-plane series magneto-resistance of the two-dimensional channel involved. So, the DOS can be obtained as well even in the quantum Hall regimes. In addition, the physical quantities obtained from the fittings, such as the subband level EO, the Fermi level EF, the 2D number de.nsity N2D and the Lande factor g*, all show oscillatory change with the magnetic field.