A method of testing a semiconductor device having a DC line configured to carry either a DC signal or a DC voltage and a circuit electrically connected to the DC line includes: during a first part of a test sequence, enabling a switch device so as to electrically connect a capacitor to the DC line via the switch device and applying a test signal to the circuit while the capacitor is electrically connected to the DC line; and during a second part of the test sequence, disabling the switch device so as to electrically disconnect the capacitor from the DC line via the switch device, injecting an AC signal onto the DC line after the capacitor is electrically disconnected from the DC line, and measuring a response of the circuit to the AC signal.