In this work, we report a gradual bipolar resistive switching memory device using Ni/Si(3)N(4/)n(+)-Si structure. Different reset transitions are observed depending on compliance current (I-COMP). The reset switching becomes abrupt around I-COMP = 10 mA, while gradual reset switching with fine controllability is preserved for the devices with I-COMP < 1 mA. We demonstrate multi-level cell (MLC) operation through the modulation of conducting path by controlling I-COMP and reset stop voltage (V-STOP) for I-COMP < 1 mA. For the devices with I-COMP = 10 mA, low resistance state (LRS) shows Ohmic behavior with metallic conducting paths, while high resistance state (HRS) shows non-Ohmic behavior. Also, it is revealed that LRS and HRS conductions follow space-charge-limited current (SCLC) mechanism in low I-COMP regime (I-COMP < 1 mA). (C) 2015 Elsevier Ltd. All rights reserved.