A semiconductor device may include a semiconductor substrate; a test circuit array region; a pad region on the semiconductor substrate and at at least a first side of the test circuit array region and outside of the test circuit array region, transistors arranged in the test circuit array region in a first direction and a second direction perpendicular to the first direction, source lines spaced apart from each other in the second direction, each of the source lines extending in the first direction and electrically connected to corresponding source electrodes of the transistors, and drain lines spaced apart from each other in the second direction, each of the drain lines extending in the first direction and electrically connected to drain electrodes of the transistors.