A semiconductor device comprises a first layer, a second layer configured to overlap with the first layer at a plurality of positions, a plurality of first layer contacts configured to be selectively activated to test the first layer for a first layer leakage current, and a plurality of second layer contacts configured to be selectively activated to test the second layer for a second layer leakage current. The first layer contacts are arranged on the first layer on a first side and a second side of the plurality of positions at which the second layer overlaps with the first layer. The second layer contacts are arranged on the second layer on a third side and a fourth side of the plurality of positions at which the second layer overlaps with the first layer. A determined first layer leakage current or second layer leakage current is indicative of the presence of a crystal defect in the semiconductor device.