A stack package includes a package substrate; a lower stack including lower dies stacked on the package substrate to form a zigzag shape in a vertical direction; an upper stack including upper dies that are sequentially offset stacked in an offset direction while providing a first upper side of a down staircase shape, a first end of an uppermost upper die among the upper dies protruding, in a horizontal direction, further than a first lower side of the lower stack; and a first passive device disposed on the package substrate and spaced apart from the first lower side, and disposed between a first portion of the package substrate and the first upper side.