A monolithic optoelectronic circuit, consisting of a GaAs light‐emitting diode (LED) driven by a Si metal‐oxide‐semiconductor (MOS) transistor, has been fabricated. Light output as a function of applied gate voltage was measured. The LED’s were fabricated in GaAs layers on Ge‐coated Si substrates containing MOS transistors. Normal transistor performance was observed after the GaAs LED fabrication, indicating that GaAs and Si processing technologies appear to be compatible.