We report on specular reflectivity measurements at the position of the waveguide at front facets of commercial diode laser arrays. Since the waveguide thickness in such semiconductor structures amounts about 1 µm an even better spatial resolution of the probe light spot is required. For this purpose, a micro-reflectance setup was designed and implemented. For re-locating the optically active region, e.g. after stepped-up operation time, we employ the photosensitivity of the active region by using the photocurrent induced by the probe beam for auto-alignment of the setup. We show for coated InGaAlAs/GaAs-'single chip' devices that during long-term operation the diode laser front facet reflectivity at the position of an emitter is almost constant with a slight tendency (about 0.002 at 633 nm) to increase. The results are explained in the framework of defect-induced refractive index changes within the semiconductor material close to the interface between waveguide and facet coating.