A method for monitoring a semiconductor fabrication process creates a wafer of semiconductor chips. Each chip has a one or more diodes. Each diode is addressable as part of an array, corresponds to a physical location of the chip, and is connected in series to a stack. The stack is composed of one ore more vertical interconnects and metal contacts. The diode and associated stack of vertical interconnects is addressed, and the current through each of the stacks of vertical interconnects in an array is measured.