We developed an impedance analyzer system with a wide frequency range for evaluating ultralow impedance. The four-point impedance measurement technique is introduced using this system. This impedance measurement can be reliably and accurately carried out by a four-point technique where one pair of contacts is used to inject a signal into the device under test (DUT), and a second pair of contacts is used to sense the resulting signal across the DUT. As a result, an evaluation system for the tens of micro-ohms of trans-impedance Z21 in the frequency range of 10 Hz to 40 GHz can be realized. By using two microwave contact probes, PDN impedance evaluation with contacted pads is realized. Therefore, the PDN impedance can be measured directly without the connectors during the measurement. Moreover, it is expected that the accurate and wideband impedance evaluation of a substrate with an electromagnetic band gap (EBG) structure can be realized.