Dielectric susceptibilities of the following semiconductors for electromagnetic field of zero frequency are investigated: InN, GaN, AlN, In x Ga1- x N, In x Al1- x N, InN containing oxygen, and non-stoichiometric InN. The real part of certain dielectric susceptibility is investigated by the electron band structure of the corresponding semiconductor. The matrix elements are calculated as terms between local wave functions describing the highest electron state of the valence band and the lowest electron state of the conduction band. The dielectric susceptibility and the corresponding dielectric permittivity are determined for semiconductors given above. The obtained results are compared with existing experimental data and good agreement is found.