Field effect transistors and methods of forming the same include forming a stack of nanowires of alternating layers of channel material and sacrificial material. A layer of sacrificial material forms a top layer of the stack. A dummy gate is formed over the stack. Stack material outside of a region covered by the dummy gate is removed. The sacrificial material is etched to form recesses in the sacrificial material layers. Spacers are formed in the recesses in the sacrificial material layers. At least one pair of spacers is formed in recesses above an uppermost layer of channel material. The dummy gates are etched away. The top layer of sacrificial material protects an uppermost layer of channel material from damage from the anisotropic etch. The sacrificial material is etched away to expose the layers of channel material. A gate stack is formed over, around, and between the layers of channel material.