The electronic structures of short-period pseudomorphically grown superlattices (SLs) of the form mInN/nGaN are calculated and the band gap variation with the well and the barrier thicknesses is discussed including hydrostatic pressure effects. The calculated band gap shows a strong dependence on the superlattice geometry. The superlattice gap vanishes for n = m ≥ 4. These effects are related to the existence of the internal electric fields that strongly influence the valence- and conduction-band profiles and thus determine the effective band gap and emission energies. The electric field strength depends strongly on the strain conditions and SL geometry, but weakly on the applied external hydrostatic pressure.