Reduction in RESET current is crucial for future high-density resistive-switching memory. We have reported a unipolar-switching Ni/HfO 2/Si structure with low RESET current of 50 μA and RESET power of 30 μW. In addition, a unique cycling evolution of RESET current across more than two orders of magnitude allows us to probe into the evolvement of filament morphology at nanoscale, using a simple yet quantitative model. Filament morphology was found to depend strongly on the charge-dissipation current proportional to the powers of SET voltage. Moreover, the formation of inactive semiconductive filaments plays an important role in the reduction in RESET current.