Monolithic electroluminescence devices require planar growth of isolated devices on a substrate. Planar growth has been realized by selective‐area molecular beam epitaxy (MBE). Selective‐area growth of ZnSe thin films by MBE has been successfully achieved over a GaAs substrate partially coated with SiO2film, where active device positions are defined by windows in SiO2layers. Extensive characterization has been carried out for both monocrystalline and polycrystalline materials. It is found that the device‐quality single‐crystal layer is isolated by the insulating polycrystalline layer. The difference in the etch rate of polycrystalline layers from that of monocrystalline layers enables the fabrication of three‐dimensional structures. Schottky barrier electroluminescence diodes have been fabricated by aninsituprocess. The diodes show white emission for applied voltages as low as 6 V.