Cu-to-Cu direct bonding was achieved at temperatures of 150-250℃ using a compressive stress of 100 psi (0.69 MPa) held for 10-60 min at 10-3 torr. The key controlling parameter for direct bonding is fast surface diffusion on (111) surfaces of Cu. Oriented (111) texture of extremely high degree, exceeding 90%, was fabricated using the oriented nanotwinned Cu. The bonded interface between two (111) surfaces forms a twist-type grain boundary. If the grain boundary has a low angle, it has a hexagonal network of screw dislocations. This technology has potential application in next-generation packaging of high-end devices.