A semiconductor device includes a first memory block including first vertical strings, a second memory block including second vertical strings coupled in series with the first vertical strings, wherein the second memory block is stacked on the first memory block, first bit lines located between the first memory block and the second memory block and electrically coupled to the first and second vertical strings, first source lines located under the first memory block and electrically coupled to the first vertical strings, and second source lines located above the second memory block and electrically coupled to the second vertical strings.