The role of surface defects on the modulated photocurrent response of the layered semiconducting compounds n-WSe2 and n-MoSe2 has been studied with the help of the scanning microscope for semiconductor characterization (SMSC). Global and localized measurements of the flatband potential V-fb have been carried out by applying the electrolyte electroreflectance method. The photocurrent images obtained at a potential close to V-fb show a significant contrast between smooth and corrugated zones. In the light of localized SMSC measurements, these results provide information about the influence of surface inhomogeneities on the semiconductor photoresponse, The enhanced interaction of I-3(-) electrolyte species with surface defects produces an improvement in photoresponse for both semiconductors. The influence of surface roughness on the position of the excitonic signal A of the tungsten semiconductor seems to indicate important differences in the anisotropic behavior of both layered compounds.