A RF MEMS switch includes a substrate, a first electrode, a first insulating layer, a second insulating layer, a second electrode and a movable electrode. The first electrode is disposed on the substrate. The first insulating layer covers the first electrode. The second insulating layer covers a portion of the substrate. The second electrode is disposed in the second insulating layer and is located at a plane different from a plane of the first electrode. The movable electrode is partially disposed on a surface of the second insulating layer, and extends over the first electrode and the second electrode. A portion of the movable electrode not disposed on the surface of the second insulating layer is a movable portion. The second insulating layer has a gap exposing a space between the movable portion and the first insulating layer and a space between the movable portion and the second electrode.