A semiconductor device includes: a substrate; a first connection structure disposed on the substrate, the first connection structure Including a first connection conductor; a transistor disposed between the substrate and the first connection structure; a first bonding structure Including a first bonding pad connected to the first connection conductor; a second bonding structure including a second bonding pad connected to the first bonding pad; a second connection structure including a second connection conductor connected to the second bonding pad; a stack structure disposed on the second connection structure; a channel structure penetrating the stack structure; and a chip guard penetrating the second connection structure, the second bonding structure, the first bonding structure, and the first connection structure, the chip guard surrounding the stack structure and the channel structure.