  From the analysis of the cyclotron resonance, we experimentally obtain the
band structure of the three-dimensional topological insulator based on a HgTe
thin film. Top gating was used to shift the Fermi level in the film, allowing
us to detect separate resonance modes corresponding to the surface states at
two opposite film interfaces, the bulk conduction band, and the valence band.
The experimental band structure agrees reasonably well with the predictions of
the $\mathbf{k\cdot p}$ model. Due to the strong hybridization of the surface
and bulk bands, the dispersion of the surface states is close to parabolic in
the broad range of the electron energies.
