Using photocurrent spectroscopy, we have studied optical absorption properties of strained InxGa1−xAs/Al0.15Ga0.85As multiple quantum wells grown by molecular beam epitaxy in the presence of electric fields perpendicular to the heterointerface. In the wavelength region where the bulk GaAs substrate is transparent, we observe the quantum confined Stark effect. Optical bistability of a self‐electro‐optic effect device is demonstrated at room temperature without removal of the GaAs substrate.