Continuous downscaling of transistor leads silicon dioxide constituting the gate in typical metal oxide semiconductor field effect (MOSFET) to its limits. One possibility is to replace SiO2 by a material of higher dielectric constant (high-k). Hafnium dioxide seems to be the most promising one. However, high-k transistor performances are often affected by the presence of defects creating charge traps or diffusion centers. In this paper, using a pseudopotential plane wave code in the density-functional total theory framework, we calculate in a monoclinic HfO2 supercell the structure, formation and ionization energies, electron affinities of intrinsic defects (oxygen vacancy and interstitial, and hafnium vacancy). We consider different charge states of these defects. The positions of defect levels with respect to the bottom of silicon conduction band are determined. Our results will be discussed and compared to literature data.