A 3-D memory is provided. Each word line layer has word lines and gaps alternately arranged along a first direction. Gaps include first group and second group of gaps alternately arranged. A first bit line layer is on word line layers and has first bit lines along a second direction. A first conductive pillar array through word line layers connects the first bit line layer and includes first conductive pillars in first group of gaps. A first memory element is between a first conductive pillar and an adjacent word line. A second bit line layer is below word line layers and has second bit lines along the second direction. A second conductive pillar array through word line layers connects the second bit line layer and includes second conductive pillars in second group of gaps. A second memory element is between a second conductive pillar and an adjacent word line.