A semiconductor structure includes a substrate, and an active device and a passive device over the substrate. The active device is disposed in a first region of the substrate, and the passive device is disposed in a second region of the substrate. The semiconductor structure further includes a shielding structure and a passivation layer. The shielding structure includes a barrier layer and a ceiling layer. The barrier layer is on the passive device and the active device, and the ceiling layer is on the barrier layer. The passivation layer is under the barrier layer and covers a top surface of the passive device. An air cavity is defined by sidewalls of the barrier layer, a bottom surface of the ceiling layer, and the substrate.