Semiconductor device structure

A semiconductor device structure includes first nanostructures formed over a substrate. The semiconductor device structure also includes a first gate structure wrapping around the first nanostructures. The semiconductor device structure also includes a first source/drain epitaxial structure formed beside the first nanostructures. The semiconductor device structure further includes a first inner spacer extending from the first gate structure to the first source/drain epitaxial structure by a first distance. The semiconductor device structure also includes second nanostructures formed over the first nanostructures. The semiconductor device structure further includes a second gate structure wrapping around the second nanostructures. The semiconductor device structure also includes a second source/drain epitaxial structure formed beside the second nanostructures. The semiconductor device structure further includes a second inner spacer extending from the second gate structure to the second source/drain epitaxial structure by a second distance, wherein the second distance is different from the first distance.