This paper reports on,in in-situ optical reflectance study of the development of the interface roughness of AlGaAs/AlAs distributed Bragg reflectors during the metalorganic vapour phase epitaxy growth of visible vertical-cavity surface-emitting laser structures. We show that the surface roughness can be extracted from time-resolved UV reflectance measurements, The roughness of the surface during growth for both the AlGaAs and AlAs layers can be determined individually. The values estimated from the in-situ optical data correlated with the roughness measured ex-situ using atomic force microscopy. The in-situ reflectance meausurement is thus shown to be a convenient noninvasive and non-destructive technique for determining surface and interface roughness even for complex device structures. (C) 2002 Elsevier Science B.V. All rights reserved.