An improved method is reported for measurements ofI‐Vcharacteristics of high‐Tcsuperconductors based upon the acquisition system developed by Kirkupetal. [Rev. Sci. Instrum.63, 2044 (1992)]. The introduction of a lock‐in mode of operation significantly enhances the voltage sensitivity in the range of relevance for the definition of the superconducting state. In addition, this approach permits the current direction in the sample to be reversed whenever needed.