The present disclosure provides a die assembly. The die assembly includes a first die, a second die and a third die stacked together. The first die includes a plurality of first metal lines facing a plurality of second metal lines of the second die, and a second substrate beneath the second metal lines faces a plurality of third metal lines of the third die. The die assembly further includes at least one first plug, a first redistribution layer and a second redistribution layer. The first plug penetrates through the second substrate to connect to at least one of the second metal lines. A first redistribution layer physically connects at least one of the first metal lines to at least one of the second metal lines, and a second redistribution layer physically connects at least one of the third metal lines to the first plug.