We present electrooptic modulation results on , A and B oriented InGaAs/GaAs multiple quantum wells. Internal electric fields are generated by a combination of strain, due to lattice mismatch, and the piezoelectric properties of III‐V semiconductors in the  structures. These fields have opposite orientation in the A and B samples. They do not occur in the  samples. The total electric field is a superposition of the strain‐generated field, the built‐in field from the p‐n junction and any externally applied field. We show that whereas in the conventional  structures the exciton energy is a quadratic function of applied field, the strain‐generated fields cause a linear shift in the exciton resonance with applied field in the  structures. In addition, the direction of the excitonic shift is opposite in the A and B samples, because the sign of the strain‐generated fields are opposite for these samples.