In accordance with an embodiment, a semiconductor device includes a substrate; a fin protruding above the substrate, the fin including a compound semiconductor material that includes a semiconductor material and a first dopant, the first dopant having a different lattice constant than the semiconductor material, where a concentration of the first dopant in the fin changes along a first direction from an upper surface of the fin toward the substrate; a gate structure over the fin; a channel region in the fin and directly under the gate structure; and source/drain regions on opposing sides of the gate structure, the source/drain regions including a second dopant, where a concentration of the second dopant in the channel region changes along the first direction, where the concentration of the second dopant at a first location within the channel region is higher than that at a second location within the channel region, where the concentration of the first dopant at the first location is lower than that at the second location. In an embodiment, the compound semiconductor material is silicon germanium, the semiconductor material is silicon, and the first dopant is germanium. In an embodiment, the channel region includes a first segment, the concentration of the first dopant in the first segment increases along the first direction, and the concentration of the second dopant in the first segment decreases continuously along the first direction. In an embodiment, the semiconductor device further includes a capping layer over the channel region of the fin, where the capping layer is substantially free of the first dopant. In an embodiment, the fin includes a first segment, the concentration of the first dopant in the first segment increases continuously along the first direction. In an embodiment, fin further includes a second segment between the first segment and the substrate, the concentration of the first dopant in the second segment is lower than a lowest concentration of the first dopant in the first segment. In an embodiment, the fin further includes a third segment between the first segment and the second segment, and the concentration of the first dopant in the third segment is uniform. In an embodiment, the concentration of the first dopant in the third segment is substantially equal to a highest concentration of the first dopant in the first segment. In an embodiment, the fin further includes a fourth segment over the first segment, with the first segment between the fourth segment and the third segment, where the concentration of the first dopant in the fourth segment is uniform. In an embodiment, the concentration of the first dopant in the fourth segment is lower than the concentration of the first dopant in the third segment. In an embodiment, the fin includes a buffer layer, a first sublayer over the buffer layer, and a second sublayer over the first sublayer, where the concentration of the first dopant in the first sublayer has a first value, the concentration of the first dopant in the second sublayer has a second value smaller than the first value, where the concentration of the first dopant in the buffer layer has a third value smaller than the second value.