A semiconductor device includes a data storage unit configured to receive input data, outputs the input data with a difference in voltage level between logic levels, and output comparison data whose logic level is distinguished from the input data; a test operation unit configured to determine a logic level of test data periodically in response to a data reference voltage whose voltage level is determined in response to a level test code during a test operation period defined by a test entry command and a test exit command, and generate a test result signal by comparing a logic level of the comparison data with the logic level of the test data; and a test operation sensing signal generation unit configured to generate a test operation sensing signal that is activated in response to the test entry command and inactivated in response to the test result signal.