The present invention provides an inline detection device for self-aligned contact defects, formed in a semiconductor substrate, comprising: an active area, formed in the semiconductor substrate, comprised of a serpentine gate having spacers on the side, a plurality of first contact windows nested immediately between the same spacers, a plurality of first contact plugs formed in the first contact windows, and two probing pads, formed in the semiconductor substrate, comprised of a plurality of matrix gates, a second contact window exposing portions of the matrix gates, and a second contact plug formed in the second contact window.