A semiconductor device structure, along with methods of forming such, are described. The structure includes a semiconductor fin including a first surface, a second surface opposite the first surface, a third surface connecting the first surface and the second surface, and a fourth surface opposite the third surface. The semiconductor device structure further includes a gate electrode layer disposed adjacent the first, third, and fourth surfaces of the semiconductor fin, a first source/drain epitaxial feature in contact with the semiconductor fin, and a first inner spacer disposed between the first source/drain epitaxial feature and the gate electrode layer. The first inner spacer is in contact with the first source/drain epitaxial feature, and the first inner spacer comprises a first material. The semiconductor device structure further includes a first spacer in contact with the first inner spacer, and the first spacer comprises a second material different from the first material.