A testing structure includes a first transistor having a first dopant type connected to a current source. The testing structure further includes a second transistor having a second dopant type, opposite to the first dopant type. The second transistor is connected to a device under test (DUT). The second transistor is connected in series with the first transistor in a cascode arrangement. The cascode arrangement is capable of measuring an output resistance of the DUT of greater than 1 mega-ohm (MΩ).