Theoretical investigations of the conduction band offset (CBO) and valence band offset (VBO) of the relaxed and pseudo-morphically strained GaAs1-xNx/GaAs1-xNy heterointerfaces at various nitrogen concentrations (x and y) within the range 0-0.05 and along the [0 0 1] direction are performed by means of the model-solid theory combined with the empirical pseudopotential method under the virtual crystal approximation that takes into account the effects of the compositional disorder. It has been found that for y < x, the CBO and VBO have negative and positive signs, respectively, whereas the reverse is seen when y > x. The band gap of the GaAs1-xNx over layer falls completely inside the band gap of the substrate GaAs1-xNy and thus the alignment is of type I (straddling) for y < x. When y > x, the alignment remains of type I but in this case it is the band gap of the substrate GaAs1-xNy which is fully inside the band gap of the GaAs I T, over layer. Besides the CBO, the VBO and the relaxed/strained band gap of two particular cases: GaAs1-xNYGaAs and GaAs1-xNx/GaAs0.98N0.02 heterointerfaces have been determined. (c) 2007 Elsevier B.V. All rights reserved.