A theoretical model was developed to simulate the apparent substrate temperature oscillation during the growth of AlAs/AlxGa1−xAs,x=0 and 0.25, distributed Bragg reflectors (DBR) for 980‐ and 780‐nm vertical cavity surface emitting lasers, respectively. The simulated data were then used forinsitumonitoring and feedback control of layer thickness by a simple pyrometric interferometry technique to obtain a highly reproducible DBR. These measurements can be performed with continuous substrate rotation and without any growth interruption. The reproducibility of the center wavelength and full width at half‐maximum of the reflectivity stop band with a variation of<±0.2% and<±0.4% for the AlAs/GaAs and AlAs/AlGaAs mirror stacks, respectively, were achieved.