A method for fabricating memory device includes: providing a substrate having a bottom electrode layer therein, forming a buffer layer and a mask layer on the buffer layer over the substrate, in contact with the bottom electrode layer, performing an advanced oxidation process on a sidewall of the buffer layer to form a resistive layer, which surrounds the whole sidewall of the buffer layer and extends upward vertically from the substrate, and forming, over the substrate, a noble metal layer and a top electrode layer on the noble metal layer, fully covering the resistive layer and the mask layer.