A modulation‐doped system of asymmetric‐coupled quantum wells is shown theoretically to possess a large optical nonlinearity due to the change transfer associated with intersubband transition. The range of parameters leading to optical bistability is detetermined. A novel triple quantum well system is suggested, allowing a few orders of magnitude reduction in switching power density. Novel hybrid optoelectronic devices, incorporating the triple quantum well system into the channel of a modulation‐doped field‐effect transistor, are proposed with potential applications as optoelectronic switches and detectors.