The present disclosure relates to a semiconductor device with an air gap below a landing pad and a method for forming the semiconductor device. The semiconductor device includes a first lower plug and a second lower plug disposed over a semiconductor substrate. The semiconductor device also includes a first landing pad disposed over a top surface and upper sidewalls of the first lower plug, and a first upper plug disposed over the first landing pad and electrically connected to the first lower plug. A width of the first lower plug is greater than a width of the first upper plug. The semiconductor device further includes a dielectric layer disposed over the semiconductor substrate. The first lower plug, the second lower plug, the first landing pad and the first upper plug are disposed in the dielectric layer, and the dielectric layer includes an air gap disposed between the first lower plug and the second lower plug.