Insitufully electrical monitoring of the reflectivity of antireflection coatings on semiconductor laser facets is experimentally demonstrated. The operating principle consists of detecting changes in the forward voltage drop induced by the modification of facet reflectivity of a constant current‐driven semiconductor laser. This technique allows one to detect the optimum thickness giving the lowest reflectivity without optical measurement. A reflectivity as low as 1×10−4was currently obtained with electron beam deposited SiOxfilms on 1.5 &mgr;m buried ridge stripe lasers.