Abstract The fundamental optical transitions in In 0.15Ga 0.85As/GaAs single symmetric quantum wells (QWs) are studied through photoreflectance (PR) measurements and their dependence on the well distance from the surface. A phase rotation of the lineshape of the PR signal is observed as was predicted in our previous works. PR spectra of several samples, measured at 77 K, are compared with results of PR lineshape calculations, and a fairly good agreement is found. The quantum-confined Stark effect is shown to be the dominant modulation mechanism in the QW. Pronounced interference effects make PR spectra from QWs sensitive to the cap layer thickness.