In this work, ultrathin HfO₂ films, less than 6 nm in thickness, are deposited by atomic-layer deposition (ALD) on Si substrates that have a variable density of silanol (Si-OH) chemical bonds after oxidizing the Si surface using hot H₂O₂. Given the surface chemistry needed for proper ALD growth of HfO₂, OH-last surfaces are needed in order to react with the Hf-based precursor during half-cycle of this reaction. The later is important for proper nucleation and uniform growth of ultrathin HfO₂ by ALD. Depending on the immersion time of an initially HF-last Si surface in hot H₂O₂, ultrathin and nonstoichiometric chemical oxides SiOx are formed presenting a variable density of Si-OH bonds which are measured after Fourier-transform infra red spectroscopy. Following SiOx formation, HfO₂ is directly deposited on these surfaces by ALD using water (H₂O) and tetrakis-dimethylamino-hafnium as precursors. Metal–insulator–semiconductor (MIS) capacitors are then formed using both HfO₂/Si and HfO₂/SiOx/Si stacked structures and their electrical characteristics are evaluated. It is found that a variable density of Si-OH chemical bonds have an impact on the physical and electrical characteristics of these MIS structures by reducing their atomic surface roughness (Rrms) and gate leakage current density (Jg), and at the same time, increasing their flat band voltage (Vfb) for the same immersion times in H₂O₂. Obtaining the lowest Rrms, Jg, and Vfb are possible by using intermediate H₂O₂ immersion times between 4 and 8 min, which is also directly related to an intermediate Si-OH bond density. © 2013 American Vacuum Society. [http://dx.doi.org/10.1116/1.4769206]