A protection structure of a pad is provided. The pad is disposed in a dielectric layer on a semiconductor substrate and the pad includes a connection region and a peripheral region which encompasses the connection region. The protection structure includes at least a barrier, an insulation layer and a mask layer. The barrier is disposed in the dielectric layer in the peripheral region. The insulation layer is disposed on the dielectric layer. The mask layer is disposed on the dielectric layer and covers the insulation layer and the mask layer includes an opening to expose the connection region of the pad.