A semiconductor structure including a test structure for detection of a gap in a conductive layer of the semiconductor structure includes a semiconductor substrate; the test structure, the test structure being located on the semiconductor substrate, the test structure comprising a multilayer gate stack, wherein the multilayer gate stack includes a single conductive layer region including: a gate dielectric located on the semiconductor substrate; the conductive layer located on the gate dielectric; and an undoped amorphous silicon layer located on the conductive layer; and wherein the test structure is configured to detect the presence of the gap in the conductive layer.