An integrated controller-modulator device, based on the enhanced Stark effect in multiquantum wells is demonstrated. The device is realised by one-step molecular beam epitaxy and selective etching of a heterojunction bipolar transistor with the quantum wells incorporated in the collector region. The device has built-in gain owing to transistor action and is cascadable, thereby lending itself to low-power photonic switching and associated optical logic applications.<<ETX>>