It is experimentally shown that the pressure applied along the twofold symmetry axis of a heterostructure with a wide GaAs/AlGaAs quantum well leads to considerable modification of the polariton reflectance spectra. This effect is treated as the stre
ss-induced decrease of the heavy-hole exciton mass. Theoretical modeling of the effect supports this assumption. The 5%-decrease of the exciton mass is obtained at pressure P=0.23 GPa.
