A package structure includes a first semiconductor package and a second semiconductor package over the first semiconductor package. The first semiconductor package includes a dielectric structure, a semiconductor device on the dielectric structure, under bump metallization (UBM) structures in the dielectric structure. The USB structures each include a first region and a second region surrounded by the first region. The first region has more metal layers than the second region. The bumps are respectively on the second regions of the UBM structures.