A semiconductor device structure, along with methods of forming such, are described. The structure includes a stack of semiconductor layers spaced apart from and aligned with each other, a first source/drain epitaxial feature in contact with a first one or more semiconductor layers of the stack of semiconductor layers, and a second source/drain epitaxial feature disposed over the first source/drain epitaxial feature. The second source/drain epitaxial feature is in contact with a second one or more semiconductor layers of the stack of semiconductor layers. The structure further includes a first dielectric material disposed between the first source/drain epitaxial feature and the second source/drain epitaxial feature and a first liner disposed between the first source/drain epitaxial feature and the second source/drain epitaxial feature. The first liner is in contact with the first source/drain epitaxial feature and the first dielectric material.