A memory device may be provided. The memory device may include a test data output circuit configured to compare lower data output from a lower data storage region with upper data output from an upper data storage region and make a decision. The memory device may include a data transmitter configured to output the lower data by inverting or noninverting the lower data according to the decision. The memory device may include a test control circuit generates a test control signal according to a test read signal and an address signal.