A memory device and a method of manufacturing the memory device includes a stacked structure having a cell region and a slimming region. The memory device also includes a plurality of vertical channel structures each including memory cells and vertically passing through the stacked structure in the cell region. The memory device further includes a plurality of support structures each having a structure of each of the vertical channel structures and vertically passing through the stacked structure in the slimming region. The plurality of support structures have different heights depending on the shape of the stacked structure in the slimming region.