For VLSI application-specific arrays and other regular VLSI circuits, two techniques are available for yield enhancement, namely defect-tolerance and layout modifications. In this paper, we compare these two yield enhancement approaches by using adders as an example. Our yield projections indicate that the layout modification technique is more efficient when the defect density is low, while reconfiguration is more efficient for a high defect density. However, from the point of the view of effective yield, the layout modification is superior to defect tolerance in the practical range of defect density.