A method of forming a semiconductor structure includes forming a dummy gate above a semiconductor substrate. The dummy gate defines a source-drain region adjacent to the dummy gate and a channel region below the dummy gate. A silicon-germanium layer is epitaxially grown above the source-drain region with a target concentration of germanium atoms. The semiconductor structure is annealed to diffuse the germanium atoms from the silicon-germanium layer into the channel region to form a silicon-germanium channel region.