We report on real-time reflectance-difference (RD) spectroscopic measurements carried out during the homoepitaxial grow of GaAs under As overpressures in the range from P-AS = 6 x 10(-7) -5 x 10(-6) Torr. We found that the time-dependent RD spectrum is described in terms of two basic line shapes. One of these components is associated to the orthorhombic surface strain due to surface reconstruction while the second one has been assigned to surface composition. Results reported in this paper render RD spectroscopy as a powerful tool for the real-time monitoring of surface strains and its interplay with surface composition during growth. (C) 2015 Elsevier B.V. All rights reserved.