SEMICONDUCTOR DEVICE

Disclosed are semiconductor devices and their fabrication methods. The semiconductor device includes a lower bonding structure that includes a lower substrate, a lower dielectric structure on the lower substrate, and a transistor between the lower substrate and the lower dielectric structure, an upper bonding structure that includes an upper dielectric structure on the lower dielectric structure, an upper substrate on the upper dielectric structure, and a memory cell structure between the upper substrate and the upper dielectric structure, a connection structure on the upper bonding structure, and a first through via that electrically connects the transistor to the memory cell structure. The transistor overlaps the memory cell structure. The first through via penetrates the upper substrate and the upper dielectric structure.