A monolithic stacked integrated circuit (IC) is provided with a known-good-layer (KGL) test circuit and a scan segment in one of its upper layers. The test circuit includes a plurality of inputs, outputs, and multiplexers coupled to the scan segment and to a second layer of the IC. The test circuit further includes a plurality of control elements such that scan testing of the stacked IC may be conducted on a layer-by-layer basis. The invention relates to a circuit and method for monolithic stacked integrated circuit testing.