A transistor array for testing is provided. The transistor array includes a plurality of tested units. Each of the tested unit includes a tested transistor and a first to third switches. The tested transistor has a control terminal, a first and a second terminals and a bulk. The first switch is coupled between the first terminal and a leakage transporting line. The second switch is coupled between the second terminal and the leakage transporting line. The third switch is coupled between the control terminal and a bias providing line. The first to third switches are turned on or turned off according to a control signal. When the tested transistor is selected to be tested, the first to third switches are turned on according to the control signal.