We investigate the reset transition of HfO2-based REAM structures with emphasis on revealing three-state resistive switching effects. We study nonpolar switching in Pt/HfO2/Pt and unipolar/bipolar switching in Pt/Ti/HfO2/Pt structures, respectively. However, three-state resistive switching is only confirmed in the former case by means of various reset methodologies. Using two-step reset experiments it is shown that the transition to the complete reset state occurs at higher voltages if the CF first drops to the intermediate state. (C) 2014 Elsevier Ltd. All rights reserved.