A silicon-based quantum dot device (1) is disclosed. The device comprises a substrate (8) and a layer (7) of silicon or silicon-germanium supported on the substrate which is configured to provide at least one quantum dot (51, 52: FIG. 5). The layer of silicon or silicon-germanium has a thickness of no more than ten monolayers. The layer of silicon or silicon-germanium may have a thickness of no more than eight or five monolayers.