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A test structure specifically designed to allow inline detection of missing spacer is introduced. Missing spacer is too small to be physically detected with any current inspection tool and therefore its existence must be flagged using voltage contrast for detection with an e-beam inspection system. The structure and methodology used to address this defect during the ramp of a recent technology is described. Key benefits include a dramatically faster learning cycle and much better signal-to-noise ratio for split experiment evaluation. Missing spacer is one example of a growing class of nonvisual defects which will greatly impact future semiconductor technologies. General principles for designing test structures to detect these defect types are discussed.