In an embodiment, a device includes: a fin on a substrate, fin having a Si portion proximate the substrate and a SiGe portion distal the substrate; a gate stack over a channel region of the fin; a source/drain region adjacent the gate stack; a first doped region in the SiGe portion of the fin, the first doped region disposed between the channel region and the source/drain region, the first doped region having a uniform concentration of a dopant; and a second doped region in the SiGe portion of the fin, the second doped region disposed under the source/drain region, the second doped region having a graded concentration of the dopant decreasing in a direction extending from a top of the fin to a bottom of the fin.