Semiconductor device and method of fabrication thereof

A method for manufacturing a semiconductor device, comprising:

• forming a trench in a stack including alternating first layers and second layers, the stack being over a substrate of the semiconductor device, and the trench having a first sidewall and a second sidewall that is opposite to the first sidewall;
• forming channel materials in the trench, the channel materials being disposed along the first sidewall and the second sidewall, respectively;
• and
• dividing the trench into multiple units by replacing portions of the channel materials with first dielectric structures, remaining portions of the channel materials along the first and second sidewalls forming first and second channel structures of first and second strings of transistors, respectively, each of the first and second strings of transistors being vertically stacked over the substrate along a vertical direction, the first strings of transistors that are along the first sidewall being separated by the first dielectric structures along a direction that is perpendicular to the vertical direction, the second strings of transistors that are along the second sidewall being separated by the first dielectric structures.