A semiconductor structure is provided. The semiconductor structure comprises a substrate, stacks, a blocking layer-trapping layer-tunneling layer structure, channel layers, a first insulating material and a dielectric layer. The stacks are formed on the substrate. Each stack comprises a group of alternating conductive strips and insulating strips as well as a first string select line formed on the group. The blocking layer-trapping layer-tunneling layer structure and the channel layers are formed conformally with the stacks. The first insulating material is formed between the stacks and covers portions of the channel layers. The dielectric layer is formed on portions of the channel layers that are not covered by the first insulating material. The semiconductor structure further comprises second string select lines formed between the stacks on the first insulating material, wherein the second string select lines are separated from the channel layers by the dielectric layer.