Embodiments of three-dimensional (3D) memory devices have a hydrogen blocking layer and fabrication methods thereof are disclosed. In an example, a 3D memory device includes a substrate, a memory stack including interleaved conductive layers and dielectric layers above the substrate, an array of NAND memory strings each extending vertically through the memory stack, a plurality of logic process-compatible devices above the array of NAND memory strings, a semiconductor layer above and in contact with the logic process-compatible devices, a pad-out interconnect layer above the semiconductor layer, and a hydrogen blocking layer vertically between the semiconductor layer and the pad-out interconnect layer and configured to block outgassing of hydrogen.