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We develop a linear-complexity direct matrix solution for the surface integral equation (IE)-based impedance extraction of arbitrarily shaped 3-D nonideal conductors embedded in a dielectric material. A direct inverse of a highly irregular system matrix composed of both dense and sparse matrix blocks is obtained in O(N) complexity with N being the matrix size. It outperforms state-of-the-art impedance solvers, be they direct solvers or iterative solvers, with fast central processing unit (CPU) time, modest memory consumption, and without sacrificing accuracy, for both small and large number of unknowns. The inverse of a 2.68-million-unknown matrix arising from the extraction of a large-scale 3-D interconnect having 128 buses, which is a matrix solution for 2.68 million right-hand sides, was obtained in less than 1.5 GB memory and 1.3 h on a single CPU running at 3 GHz.