A testkey design pattern includes a least one conductive contact, at least one conductive line of a first width vertically and electrically connected to the conductive contact, and at least one pair of source and drain respectively directly connected to each side of the conductive line. The pair of source and drain and part of the conductive line of a first length directly connected to the source and drain form an electronic device. The testkey design patterns are advantageous in measuring capacitance with less error and for better gate oxide thickness extraction.