The microstructure and resistive switching of HfOx deposited onto a TiN bottom electrode (BE) treated with and without chemical-mechanical polishing (CMP) were investigated. The crystallinity of the HfOX film above a CMP BE is less than that above a regular BE. The CMP-treated BE leads to HfOX devices with high forming voltage, low leakage current in the initial state, low magnitude of the first low-resistance state, and high resistivity in high-resistance state. Current overshoot during the SET step may deteriorate performance of the HfOX devices to be unswitchable after enduring 400 cycles. A possible mechanism for this deterioration and the solution to recover the device endurance are proposed. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.001205esl] All rights reserved.