A semiconductor device including a first structure including a first conductive pattern, the first conductive pattern exposed on an upper portion of the first structure, a mold layer covering the first conductive pattern, a second structure on the mold layer, and a through via penetrating the second structure and the mold layer, the through via electrically connected to the first conductive pattern, the through via including a first via segment in the second structure and a second via segment in the mold layer, the second via segment connected to the first via segment, an upper portion of the second via segment having a first width and a middle portion of the second via segment having a second width greater than the first width may be provided.