The time-dependences of leakage currents due to electrons and holes flowing through HfO2-based high-k gate dielectric films under constant voltage stresses are investigated by a carrier separation method using field-effect transistor structures. In the case of balanced injection, some of the injected electrons were trapped near the gate, while some of the injected holes were trapped near the substrate. As a result, both leakage currents reduced. Capacitance change during the relaxation after the removal of the gate voltage stress supported the leakage current change. The relationship between the electron-/hole-trapping centers and oxygen-related defects in high-k dielectric films is discussed. 2005 IEEE.