In 1984 we at GEC decided to establish a research group on superlattices, that is multilayer semiconductor structures, using GaAs and the AlGaAs alloys. We perceived three physics principles to be ripe for novel exploitation: tunnelling through thin barriers; hot electron injection from heterojunctions; and carrier confinement in thin layers. The high electron mobility field effect transistor and the quantum well laser, both using the last of these three principles, had already been proven in the laboratory, and since then both have become commercial products. After five years, the second of these principles has led to a new product, a hot-electron injected Gunn diode, which we describe here, while our research on the other two also seems set to emerge into new products.