Reliable and precise knowledge about the strain and composition effects on the electronic properties is crucial for the optimization of III-nitride based heterostructures for electronic and optoelectronic device applications. Using the nearest neighbor sp(3)s* semi-empirical tight binding formalism, we investigated the composition effects on bandgaps and offsets in pseudomorphic InGaN/GaN and GaAsN/GaAs heterostructures with zinc-blende structures. The strain effects are incorporated afterwards in a semi-empirical way. The model should be useful in understanding the effects of composition and strain on heterostructure energy band properties. (C) 2004 Elsevier Ltd. All rights reserved.