This fast hierarchical circuit extractor for the Magic VLSI layout system derives its speed from its ability to handle hiearchicalarrays, and from a new algorithm based on corner-stitching, a geometrical data structure for representing Manhattan shapes.Corner-stitching's ability to find adjacent mask information is critical to the basic extractor speed, and its ability tosearch areas makes the hiearchical extraction algorithm practical. The extractor is incremental, necessitating re-extractionof only a few cells after a layout is modified. It accepts a hierarchical layout that may contain nearly arbitrary overlapsbetween cells, and produces a circuit description with the same hierarchical structure as the layout. The extractor can completelyextract a 37,000-transistor chip in 20 minutes of VAX CPU time, or incremetally in an average of 8 minutes. The extractorprocesses 50-65 FETS per second on a VAX-11/780 running Unix. if only substrate capacitance is being extracted. If couplingcapacitance is also extracted, the basic extractor processes 25-35 transistors per second.