Conventional thermal annealing with various caps on the surface of the sample is used to selectively disorder one section of a multiple quantum well GaAs/AlGaAs structure. In the disordered section, the shift of the photoluminescence peak is in the range where the chirp parameter (ratio of real index change over absorption change) is large at the laser wavelength in the undisordered material. Moreover, photoconductivity measurements on samples under reverse bias, as well as laser testing, prove that the electric properties are preserved by the thermal treatment. Therefore, the investigated process should be highly suitable for the monolithic integration of a laser and phase modulator.