The effects of defect-enhanced, impurity-free, quantum-well (QW)-barrier compositional intermixing caused by the SiO2cap annealing at 750 °C of a 1.5-&mgr;m InGaAsP/InP multiple quantum-well (MQW) laser structure have been studied by photoluminescence (PL). A substantial band-gap blue shift, as much as 112 nm(∼66 meV), was found in the structure and the value of the shift can be controlled by the anneal time. The amount of the shift does not depend on the thickness of the SiO2cap layer. Ridge-waveguide lasers were fabricated on the different areas of the wafer, with and without a SiO2cap during a 60 s anneal. The lasing wavelength of the laser produced with the SiO2cap has a 78 nm blue shift over that of the laser without the SiO2cap. ©1997 American Institute of Physics.