Disclosed is a method of forming planar and non-planar semiconductor devices using a sacrificial gate sidewall spacer with a uniform vertical thickness. The method forms such spacers by selectively growing an epitaxial film on the vertical sidewalls of a gate structure. The use of an epitaxial growth process, as opposed to a deposition and etch process, ensures that the resulting spacers will have a uniform vertical thickness. Then, any process steps (e.g., implant and/or etch process steps) requiring the use of the gate sidewall spacers (e.g., as a mask or shield) are performed. Precise implant and/or etch profiles can be achieved, during these process steps, as a function of the uniformity of the gate sidewall spacers. Once such process steps are completed, the sidewall spacers are selectively removed. Optionally, before removing the sidewall spacers, they can be oxidized in order to enhance the selective removal process.