An RRAM device is provided, which includes a bottom electrode in an oxide layer, a plurality of dielectric protrusions on the oxide layer, wherein the bottom electrode is disposed between the two adjacent dielectric protrusions. A resistive switching layer is conformally disposed on the dielectric protrusions, the oxide layer, and the bottom electrode. A conductive oxygen reservoir layer is disposed on the resistive switching layer, and an oxygen diffusion barrier layer is disposed on the conductive oxygen reservoir layer.