A die stack includes: a first die including a first semiconductor substrate; a second die including a second semiconductor substrate; a bonding dielectric structure including a bonding polymer and that bonds the first die and the second die; a bonding interconnect structure that extends through the bonding dielectric structure to bond and electrically connect the first die and the second die; and a bonding dummy pattern that extends through the bonding dielectric structure to bond the first die and the second die. The bonding dummy pattern is electrically conductive and is electrically floated.