A semiconductor device is fabricated by providing a substrate including a silicon channel layer and a silicon-germanium channel layer, forming gate structures disposed on the silicon channel layer and on the silicon-germanium channel layer, forming a first protection layer to cover the resultant structure including the gate structures, and injecting hydrogen and/or its isotopes into the silicon-germanium channel layer. The silicon and silicon-germanium channel layers may be oriented along a direction. Related devices are also described.