We have investigated in situ monitoring of growth rate and composition by reflection measurements during AlGaInP and InGaAsP growth in metalorganic vapor phase epitaxy. The reflection transient shows Fabry-Perot oscillations during epitaxial growth, and analysis of this oscillation gives the optical constants of AlGalnP and InGaAsP at a growth temperature. By using the relationship between the optical constants and the composition of epitaxial layer, in situ monitoring of growth rate and composition are realized for a variety of structures. The growth rate and the composition of AlGaInP and InGaAsP, which are obtained by using our proposed in situ monitoring method, are in good agreement with those estimated by conventional ex situ measurements such as thickness, XRD and PL measurement. (c) 2005 Elsevier B.V. All rights reserved.