Short-period superlattice minibands have been studied by ballistic electron luminescence spectroscopy. Using a combination of optical and electrical measurements in a single device, electron transport through an AlGaAs/GaAs superlattice was observed. The optical measurement provided a precise energy scale for calibration of voltages obtained in the electrical experiment. A three terminaln-p-pdevice was used, where the electrons were injected through an emitter-base tunnel barrier into ap-type base, which was separated from thep-doped collector by a superlattice. Luminescence emitted by ballistic electrons recombining in the base was used to measure their kinetic energy. Oscillations in the transistor gain were detected and are due to transport through the superlattice miniband. ©1997 American Institute of Physics.