Embodiments of three-dimensional (3D) memory devices having through stair contacts (TSCs) and methods for forming the same are disclosed. In an example, a 3D memory device includes a memory stack and a TSC. The memory stack includes a plurality of interleaved conductive layers and dielectric layers. Edges of the interleaved conductive layers and dielectric layers define a staircase structure on a side of the memory stack. The TSC extends vertically through the staircase structure of the memory stack. The TSC includes a conductor layer and a spacer circumscribing the conductor layer.