Bump shapes are determined by the current distributions of the cathodes. These current distributions are discussed both by experiments and numerical computations. The potentials are classified by linear, Tafel and diffusion control regions. At the linear region, the current distributions are uniform because of the large surface over potential. The growth rates are slow. At the Tafel region, the distributions are not uniform because of large ohmic resistance. The cavity edges show hump for larger cavity widths of more than 100 mu m. For smaller widths, the current distributions become uniform and the hump forms at the centers. At the diffusion controlled region, the current distribution is determined by the vortices. The vortices act as the resistance of mass transfer to the cathode. For the 100 mu m cavity width, the vortices grow at the up stream corner with high Peclet numbers of 1410 and 7311. The current distributions show hollows at the up stream corners. The vortices become smaller at down stream corners. These smaller vortices cause the increase in current distributions at down stream. For 30 mu m cavity width, on the other hand, a large single vortex forms for the higher Peclet number of 44500 and a single hump in current distribution is achieved.