Semiconductor device having three-dimensional cell structure

A semiconductor device comprising:

• a substrate;
• a plurality of word line structures disposed over the substrate to be spaced apart from each other in a first direction perpendicular to a surface of the substrate, each of the plurality of word line structures extending in a second direction parallel to the surface of the substrate;
• a switching layer disposed over the substrate to contact side surfaces of the plurality of word line structures;
• and
• bit line structures disposed over the substrate to extend in the first direction and to contact a surface of the switching layer,
• wherein the switching layer is configured to perform a threshold switching operation and has a variable programmable threshold voltage,
• wherein a first contact surface of the switching layer that the switching layer contacts the side surfaces of the plurality of word line structures has substantially right angle with the substrate, and a second contact surface of the switching layer that the switching layer contacts side surfaces of the bit line structures has acute angle with the substrate.