Hafnium oxide (HfO2) is a potential material for equivalent oxide thickness (EDT) scaling in microelectronics; however, its surface passivation properties particularly on silicon are not well explored. This paper reports investigation on passivation properties of thermally deposited thin HfO2 films by atomic layer deposition system (ALD) on silicon surface. As-deposited pristine film (similar to 8 nm) shows better passivation with <100 cm/s surface recombination velocity (SRV) vis-a-vis thicker films. Further improvement in passivation quality is achieved with annealing at 400 degrees C for 10 min where the SRV reduces to similar to 20 cm/s. Conductance measurements show that the interface defect density (D-it) increases with film thickness whereas its value decreases after annealing. XRR data corroborate with the observations made by FTIR and SRV data. (C) 2015 Published by Elsevier B.V.