Continuous in situ X-ray reflectivity (XRR) measurements were used to investigate the growth process of an In0.11Ga0.89N epilayer and its single quantum well grown on c-plane GaN/sapphire templates using an in-house-designed metalorganic vapor phase epitaxy installed in a laboratory-grade X-ray diffractometer. The surface roughening of the epilayer as a function of growth time was calculated from the continuous in situ XRR curve. The growth rate, critical thickness h(c(r)) for surface roughening, and roughening rate were obtained. The experimental critical thickness h(c(r)) of the In0.11Ga0.89N epilayer analyzed from the continuous in situ XRR curve was 14.8 +/-, 0.4 nm. Based on the calculated theoretical critical thickness h(c) and the experimental h(c(r,2)), Fischer's model seems to be appropriate for describing the critical thickness of the InGaN/GaN. (C) 2014 Elsevier By. All rights reserved.