A robust gate spacer that can resist a long overetch that is required to form gate spacers in fin field effect transistors (FinFETs) and a method of forming the same are provided. The gate spacer includes a first gate spacer adjacent sidewalls of at least one hard mask and a top portion of sacrificial gate material of a sacrificial gate structure and a second gate spacer located beneath the first gate spacer and adjacent remaining portions of sidewalls of the sacrificial gate material. The first gate spacers is composed of a material having a high etch resistance that is not prone to material loss during subsequent exposure to dry or wet etch chemicals employed to form the second gate spacer and to remove the hard mask.