Electrical spin-injection across the Fe3O4:Al0.1Ga0.9As interface has been measured. We quantify this effect in an In0.2Ga0.8As:GaAs spin-light emitting diode optical device. The optical polarization signal is maintained from 4.2 up to 200 K without influence of the metal–insulator Verwey transition in the bulk of the Fe3O4 film. An incomplete oxidation at the interface may be detrimental for this device, as it has a similar spin-injection efficiency to that of Fe:Al0.1Ga0.9As. Ambient temperature operation of this device may be possible although the present polarization levels remain too low for practical spintronic applications. We demonstrate the first step in the integration of molecular beam epitaxy-grown magnetic oxides into III–V semiconductor devices.