In an embodiment, a device includes a substrate, a first semiconductor layer that extends from the substrate, and a second semiconductor layer on the first semiconductor layer. The first semiconductor layer includes silicon and the second semiconductor layer includes silicon germanium, with edge portions of the second semiconductor layer having a first germanium concentration, a center portion of the second semiconductor layer having a second germanium concentration, and the second germanium concentration being less than the first germanium concentration. The device also includes a gate stack on the second semiconductor layer, lightly doped source/drain regions in the second semiconductor layer, and source and drain regions extending into the lightly doped source/drain regions.