Аннотация:The Landau level spectroscopy technique has been used to explore the electronic structure of the 20 nm HgTe quantum wells known for their semimetallic behaviour. THz absorption observed not only as classical cyclotron resonance but also in quantized magnetic fields due to inter-Landau levels transitions originated from the valence band. The obtained results were interpreted within the 8×8 k∙p model, particular magneto-optical transitions are followed up to the magnetic field of 34 T.