In accordance with an embodiment, a semiconductor device includes a fin over a substrate, the fin including silicon germanium; a gate structure over the fin; a channel region in the fin, the gate structure being disposed over the channel region, a concentration of germanium in the channel region changing along a first direction from an upper surface of the fin distal the substrate to the substrate, where a concentration of germanium increases from a first location of the channel region to a second location of the channel region, where the first location and the second location are aligned along the first direction; and a source/drain region in the fin and adjacent to the gate structure, the source/drain region including a dopant, a concentration of the dopant in the channel region changing along the first direction, where a concentration of the dopant decreases from the first location of the channel region to the second location of the channel region. In an embodiment, the dopant is boron or antimony. In an embodiment, the source/drain region includes a first sublayer, a second sublayer over the first sublayer, and a third sublayer over the second sublayer, where the first sublayer has a first concentration of the dopant, the second sublayer has a second concentration of the dopant, and the third sublayer has a third concentration of the dopant, where the third concentration is higher than the second concentration, and the second concentration is higher than the first concentration. In an embodiment, the fin includes a gradient layer, where the concentration of germanium in the gradient layer increases along the first direction. In an embodiment, the fin further includes a buffer layer between the gradient layer and the substrate, where the concentration of germanium in the buffer layer is lower than the concentration of germanium in the gradient layer.