A method includes depositing a mask layer over a semiconductor substrate, etching the mask layer to form a patterned mask, wherein a sidewall of the patterned mask includes a first sidewall region, a second sidewall region, and a third sidewall region, wherein the first sidewall region is farther from the semiconductor substrate than the second sidewall region and the second sidewall region is farther from the semiconductor substrate than the third sidewall region, wherein the second sidewall region protrudes laterally from the first sidewall region and from the third sidewall region, etching the semiconductor substrate using the patterned mask to form fins, forming a gate stack over the fins, and forming source and drain regions in the fin adjacent the gate stack.