Semiconductor devices and methods of forming the same include forming an inner spacer on a semiconductor fin. Two outer spacers are formed around the inner spacer, with one outer spacer being in contact with the inner spacer and with the other outer spacer being separated from the inner spacer by a gap. A dipole-forming layer is formed on the semiconductor fin in the gap. The inner spacer is etched away. A gate stack is formed on the semiconductor fin, between the outer spacers.