In this paper, we present an attractive approach of argon plasma-induced quantum well intermixing for InP based heterostructures. The lattice-matched five quantum wells of InGaAs/InGaAsP grown by MOVPE exhibited a large blue shift with minimal line width broadening after plasma exposure and annealing. This large shift occurs due to interdiffusion of high density of point defects created by high ion current density in the inductively coupled plasma system. The interdiffusion creates a high degree of intermixing, with coherent diffusion of the group III and group V elements on their own sublattices. Intermixing results in no material quality degradation that highlights the plasma quantum well intermixing technique is well suited for photonic integration circuit fabrication. (C) 2004 Published by Elsevier B.V.