Reactive ion etching (RIE) has been combined with laser interferometry at 905 nm as an in situ diagnostic technique for the fabrication of laser mirrors for GaAs/AlxGa1-xAs laser diodes. The laser structure was a graded-index separate confinement multiple quantum well heterostructure and the mirrors were formed with an optimized BCl3 RIE process. The laser interferometry was used for real-time identification of heterointerfaces, monitor of the etch rate, end point control and detection of the development of roughness during the dry etching process of the GaAs/AlxGa1-xAs laser diodes. It has been demonstrated that the relatively simple technology of RIE assisted by laser interferometry at 905 nm for in situ etching control is capable of the engineering of complex processes and the fabrication of advanced photonic circuits.