A semiconductor device includes a device layer, a first passivation layer, an aluminum pad, a second passivation layer, an under-ball metallurgy (UBM) pad and a connector. The device layer is disposed over a substrate, wherein the device layer includes a top metal feature. The first passivation layer is disposed over the device layer. The aluminum pad penetrates through the first passivation layer and is electrically connected to the top metal feature. The second passivation layer is disposed over the aluminum pad. The UBM pad penetrates through the second passivation layer and is electrically connected to the aluminum pad. The connector is disposed over the UBM pad. In some embodiments, a first included angle between a sidewall and a bottom of the aluminum pad is greater than a second included angle between a sidewall and a bottom of the UBM pad.