An apparatus has a first gate structure of a core device on a substrate, a first L-shaped spacer covering a sidewall of the first gate and part of the substrate adjacent to the first gate, a first raised source/drain (S/D) structure on the substrate and spaced apart from the first gate by the first L-shaped spacer, a second gate of an I/O device on the substrate, a second L-shaped spacer covering a sidewall of the second gate and part of the substrate adjacent to the second gate, and a second raised S/D structure spaced apart from the second gate by the second L-shaped spacer. The first and second L-shaped spacers have the same spacer width, and a distance between the first gate structure and a sidewall of the first S/D structure is less than a distance between the second gate structure and a sidewall of the second S/D structure.