A capacitive electro-optical modulator includes a silicon layer having a cavity having sidewalls and a floor. A germanium or silicon-germanium strip overlies the silicon layer within the cavity. A silicon strip overlies the germanium or silicon-germanium strip within the cavity. The silicon strip is wider than the germanium or silicon-germanium strip. An insulator fills the cavity laterally adjacent the germanium or silicon-germanium strip and the silicon strip and extending between the sidewalls of the cavity. An upper insulating layer overlies the silicon strip and the insulator. A layer of III-V material overlies the upper insulating layer. The layer of III-V material formed as a third strip is arranged facing the silicon strip and separated therefrom by a portion of the upper insulating layer.