Embodiments of the present invention provide a test structure for inspection of integrated circuits. The test structure may be fabricated on a semiconductor wafer together with one or more integrated circuits. The test structure may include a common reference point for voltage reference; a plurality of voltage dropping devices being connected to the common reference point; and a plurality of electron-collecting pads being connected, respectively, to a plurality of contact points of the plurality of voltage dropping devices. A brightness shown by the plurality of electron-collecting pads during an inspection of the integrated circuits may be associated with a pre-determined voltage.