A method includes etching a substrate to form a semiconductor fin, forming a gate stack on a top surface and sidewalls of the semiconductor fin, and forming a first recess in the semiconductor fin on a side of the gate stack, wherein forming the first recess comprises, performing a first etching process to form a first portion of the first recess, depositing a first dielectric layer on sidewalls of the gate stack and the first portion of the first recess, performing a second etching process to form a second portion of the first recess using the first dielectric layer as a mask, wherein the second portion of the first recess extends under the gate stack, and performing a third etching process to remove the first dielectric layer.