Abstract: A dynamic calibration technique so-called "calibration-on-the-fly (COF)" for on-wafer measurement at millimeter-wave is demonstrated in order to correct of crosstalk or leakage error between probes which conventional calibration methods failed to deal with. In the COF technique, a new error model is developed that treats the leakage error separately from calibration and the measuring of wafer devices. With a dummy calibration standard pair e.g., open-open pair or load-load pair, the leakage error can be correctly measured during system calibration and removed during wafer measurements. Thus, the accuracy of the test result can be improved by 10%. Besides, a short-short pair should not be used as a dummy pair because singularity will be generated when solving equations based on the technique.