The present technology includes a semiconductor memory device and a method of manufacturing the same. The semiconductor memory device includes a first semiconductor layer, a cell stack and a peripheral stack each disposed on the first semiconductor layer, a first slit structure extending in a first direction and penetrating the cell stack and the peripheral stack, a penetration structure penetrating the peripheral stack and being spaced apart from the first slit structure, and a support structure penetrating the peripheral stack. The support structure includes first sidewall portions spaced apart from each other and a second sidewall portion connecting the first sidewall portions to each other, and the penetration structure is disposed between the first sidewall portions.