We fabricate ultra-thin HfO₂ gate stacks of very high permittivity value by using atomic layer deposition (ALD) and Ti-cap post deposition annealing. The HfO₂ layer is directly deposited on hydrophilicized Si surface by ALD. A cubic crystallographic phase is generated in ALD-HfO₂ by short time annealing with Ti capping layer. The Ti layer absorbs residual oxygen in HfO₂ layer. The reduced oxygen concentration during annealing suppresses the growth of the interfacial SiO₂ layer. The dielectric constant of ALD-HfO₂ is enhanced to ～40, and extremely scaled ～0.2 nm equivalent oxide thickness of total gate stack is obtained.