The planar radius and the binding energy of excitons in extremely shallow quantum well (ESQW) structures are calculated theoretically. As the strength of an applied electric field increases, the exciton planar radius increases and the binding energy decreases rapidly compared with a conventional quantum well, which explains the rapid peak quench in ESQW structures. We also calculate the energy difference between heavy hole and light hole exciton transitions in quantum wells with various barrier heights. Due to the small energy difference in ESQW structures, the light hole peak is not clearly resolved from heavy hole peak by room‐temperature photocurrent experiments. ©1996 American Institute of Physics.