Metal-organic vapor phase epitaxial growth of GaAsN quantum wells is monitored by in situ reflectance measurements. Correlation between the change in the reflectance intensity and nitrogen content of the quantum well is established. The reflectance as a function of time also reveals if there is deterioration of the crystalline quality during growth. This method together with X-ray diffraction and photoluminescence characterization is applied to analyze GaAsN growth using various reactor pressures and TBAs/III molar flow ratios. (c) 2006 Elsevier B.V. All rights reserved.