We report experimental results from temperature dependence studies of the optical absorption edge of the GaNP alloys with N compositions up to 3.1 %. The observed increase in the absorption coefficient with increasing N content, as well as the spectral shape of the absorption edge incline a band crossover to a direct band gap for the alloy, in agreement with previous studies. Temperature variation of the GaNP band gap, however, is found to be rather similar to that in the parental GaP, except for the N composition of similar to1% when a slow down in the thermally induced reduction of the band gap energy was observed due to a resonant interaction with the N-related defects. We thus suggest that both contributions from the interaction with the localized states and the increasing F character of the conduction band states are important for the alloy formation. (C) 2002 Elsevier Science Ltd. All rights reserved.