We report the use ofinsitureflectance spectroscopy for real‐time monitoring of the metalorganic vapor phase epitaxy (MOVPE) growth of InGaAsP films.Insituoptical measurements have not been previously reported for this materials system because of its strong absorption in the spectral range of commonly available detectors (&lgr;<1100 nm). To acquire reflectance data beyond the absorption regions of these films we used a grating spectrometer with a Si/PbS dual detector having a wavelength range of 400–2500 nm. Measurements were made during growth of InP/InGaAs/InP double heterostructures and 1.3 &mgr;m InGaAsP MQW laser device structures. The multiwavelength reflectance data enabled extraction of the film optical constants, determination of deposition rates to better than 1%, and provided nanometer scale thickness sensitivity for MQW samples. ©1996 American Institute of Physics.