A method includes forming a first gate structure over a substrate, where the first gate structure is surrounded by a first dielectric layer; and forming a mask structure over the first gate structure and over the first dielectric layer, where forming the mask structure includes selectively forming a first capping layer over an upper surface of the first gate structure; and forming a second dielectric layer around the first capping layer. The method further includes forming a patterned dielectric layer over the mask structure, the patterned dielectric layer exposing a portion of the mask structure; removing the exposed portion of the mask structure and a portion of the first dielectric layer underlying the exposed portion of the mask structure, thereby forming a recess exposing a source/drain region adjacent to the first gate structure; and filling the recess with a conductive material.