A capacitive electro-optical modulator includes a silicon layer, a germanium or silicon-germanium strip overlying the silicon layer, and a silicon strip overlying the germanium or silicon-germanium strip. The silicon strip is wider than the germanium or silicon-germanium strip. An insulator is laterally adjacent the germanium or silicon-germanium strip and the silicon strip and has an upper surface that is flush with an upper surface of the silicon strip. An insulating layer overlies the insulator and the silicon strip. A layer of III-V material overlies the insulating layer. The layer of III-V material is formed as a third strip arranged facing the silicon strip and separated therefrom by a portion of the insulating layer.