Hafnium oxide (HfO2) is currently considered to be a good candidate to take part as a component in charge-trapping nonvolatile memories. In this work, the electric field and time dependences of the electron trapping/detrapping processes are studied through a constant capacitance voltage transient technique on metal-oxide-semiconductor capacitors with atomic layer deposited HfO2 as insulating layer. A tunneling-based model is proposed to reproduce the experimental results, obtaining fair agreement between experiments and simulations. From the fitting procedure, a band of defects is identified, located in the first 1.7nm from the Si/HfO2 interface at an energy level Et=1.59eV below the HfO2 conduction band edge with density Nt=1.36×1019cm−3. A simplified analytical version of the model is proposed in order to ease the fitting procedure for the low applied voltage case considered in this work.