We report the growth and characterization of InxAl1−xAs/InP heterostructuresgrown by organometallic molecular‐beam epitaxy. X‐ray rocking curves with half‐widths as low as 53 arc sec and low temperature photoluminescencelinewidths of 26 meV were obtained for the InAlAs layers near lattice‐matched to InP. The interface quality was investigated by photoluminescence taking advantage of the type II nature of the interface.Interface quality was improved by reducing the length of the growth halt between layers. The important effects of interface chemistry were studied, and in fact, quality was enhanced by introducing binary interfacial layers only 1 ML in thickness.