Sidewall spacers are disclosed that extend on opposing sidewalls of gate stacks. The sidewall spacers have improved profiles to suppress or eliminate void formation between the gate stacks during gap-filling A gate dielectric layer is formed on a semiconductor substrate. Then, a gate stack 24 having a sidewall is formed over the gate dielectric layer. The gate stack 24 comprises a conductive layer 28 and a hard mask 30 overlying the conductive layer 28. A liner 32 is selectively deposited over the gate stack 24 such that the liner 32 is deposited on the hard mask 30 at a rate lower than the rate of deposition on the conductive layer 28. Thus, the liner 32 is substantially thinner on the hard mask 30 than on the conductive layer 28. A nitride spacer is formed over 34 the liner 32. A PMD layer is formed over the resultant structure, filling the gaps between adjacent gate stacks.