In this paper, we report the fundamental properties of NiOx based Resistive RAM (RRAM) devices with Al top electrode and Ni bottom electrode. The NiOx deposition was performed in a relatively high oxygen environment. The initial J-V curves in positive and negative bias indicated symmetric behavior in spite of a significant difference in the vacuum work functions of Al and Ni. The capacitance-voltage characterizations indicated NiOx to be a p-type semiconductor with acceptor doping density between 6 x 10(18) cm(-3) and 5 x 10(20) cm(-3). Switching behavior was observed after electroforming the devices. The devices failed after multiple switching cycles by switching into a relatively low conductive state. The mechanism of failure was attributed to the formation of Al2O3 due to a slow oxidation of Al electrodes with repeated cycles. (C) 2011 Elsevier Ltd. All rights reserved.