The effects of the distribution of power and ground vias in C4/BGA type of packages are studied. Two types of via distributions are evaluated. One type is that vias are concentrated in the core area. The other type is that vias are uniformly distributed across the package. The performances of power and ground supplies of packages are evaluated through their resonance characteristics, impedances and effective inductances. It is found that the lowest package resonant frequency is increased by adding power and ground vias in the package. It is also found that, there are no significant differences in the lowest resonant frequencies between the two types of via distributions, but the centered via distribution results in substantially lower effective inductance of the package.