The dielectric properties and n-type metal oxide semiconductor field-effect transistor (nMOSFET) positive bias temperature instability (PBTI) characteristics of in situ nitrogen-incorporated plasma-enhanced atomic layer deposited HfOxNy gate dielectrics were compared with those of the HfO2 films. Although the physical thickness of the HfOxNy and HfO2 films were almost identical (similar to 4.1 nm), the capacitance equivalent oxide thickness of HfOxNy (1.43 nm) was much lower than that of HfO2 (2.28 nm), suggesting that HfOxNy has a larger dielectric constant. However, HfOxNy showed a higher leakage current than HfO2 due to a decrease in bandgap. HfOxNy showed a turnaround effect under a positive gate stress bias in nMOSFET. The threshold voltage (V-th) shifted to the positive direction during the first second due to the trapping of electrons at pre-existing trap sites in Hf-based gate dielectrics. Subsequently, the V-th shifted in the negative direction due to hole trapping, which originated from the generation of electron-hole pairs related to the surface plasmon. HfOxNy showed a higher initial interface trap density but a lower interface trap generation rate during n-type MOS PBTI stress than HfO2.