Abstract: Semiconductor fabrication methods and semiconductor devices are disclosed. According to some aspects, a memory device includes a memory stack having interleaved a plurality of conductive layers and a plurality of insulating layers on a substrate, and a channel structure extending vertically in the memory stack. The channel structure includes a semiconductor channel extending vertically in the memory stack and conductively connected to a source structure. The semiconductor channel includes polysilicon, and a grain size of the polysilicon ranges from 100 nm to 600 nm.