Sensing of the I-V characteristics of two terminals with negative dynamic resistance may be practically impossible with the instrumentation, which functions well for devices exhibiting positive only dynamic resistance. This is due to tendency to oscillate when connected into the sensing circuit, especially if the DUT (Device under Test) is a fast-switching one e.g. tunnel diode or Gunn diode. In the next a method and means allowing sensing of I-V characteristics of devices with negative dynamic resistance within “lying S”-type of I-V curve are described.