Structures for spacers of a field-effect transistor and methods for forming such spacers. A mask layer has a feature separated from a vertical sidewall of a first gate structure by a space of predetermined width that exposes a top surface of a semiconductor body. A spacer is formed adjacent to the vertical sidewall of the first gate structure. The spacer has a first section in the space and a second section. The first section of the spacer is located vertically between the second section of the spacer and the top surface of the semiconductor body. The first section of the spacer extends through the space to the top surface of the semiconductor body, and the first section of the spacer fully fills the space.