Abstract-While it is important to exhaustively verify IC designs for their functional performance, it is equally important to verify their robustness against spot defects, that is, to foresee what will happen to the design when it is exposed to defect conditions in a real manufacturing environment. One such verification is done by extracting the layout sites sensitive to defects. These sites are the places where defects can induce a functional failure of the design. Initial attempts to perform this verification task were based on a "critical area extraction" of one layer at a time. However, this extraction neglects the electrical significance of interrelationships between layers, as could be the case with transistors, vias, etc. In this paper we present a novel method to construct deterministically multilayer critical areas. These critical areas are established on the theoretical basis of defect semantics and on the new concept of "susceptible sites." Based on these foundations, we developed a system comprising several algorithms which in principle maintain simultaneously as many scan lines as the number of layers, in such a way that it is possible to keep track of the vertical and horizontal effects of defects. The paper also presents experimental timing results and a case study for diagnosing defect-fault information on an IC.