A semiconductor device structure, along with methods of forming such, are described. The structure includes first and second source/drain epitaxial features, a first gate electrode layer disposed between the first and second source/drain epitaxial features, third and fourth source/drain epitaxial features, a second gate electrode layer disposed between the third and fourth source/drain epitaxial features, fifth and sixth source/drain epitaxial features disposed over the first and second source/drain epitaxial features, and a third gate electrode layer disposed between the fifth and sixth source/drain epitaxial features. The third gate electrode layer is electrically connected to the second source/drain epitaxial feature. The structure further includes a seventh source/drain epitaxial feature disposed over the third source/drain epitaxial feature and an eighth source/drain epitaxial feature disposed over the fourth source/drain epitaxial feature. The second gate electrode layer is disposed between the seventh and eighth source/drain epitaxial features.