A semiconductor device structure is provided. The semiconductor device structure includes a substrate having a plurality of nanowires over an input-output region, and a protective layer surrounding the nanowires. The protective layer is made of silicon, silicon germanium, silicon oxide, silicon nitride, silicon sulfide, or a combination thereof. The semiconductor device structure also includes a high-k dielectric layer surrounding the protective layer, and a gate electrode surrounding the high-k dielectric layer. The semiconductor device structure further includes a source/drain portion adjacent to the gate electrode, and an interlayer dielectric layer over the source/drain portion.