A chip structure can reduce the phenomenon of overcrowding current at the conventional circular opening of the passivation layer and further causing electromigration when the current flows to the bonding pad via the transmission line. The improved structure for the side profile of the opening of the passivation layer is about a circular profile, but the portion near to the transmission line is a straight line or a curving line. When the current flows through this opening, the current density can be uniformly distributed along the straight line or the curving line, and whereby the phenomenon of overcrowding current can be reduced.