The protection performance of an electrostatic-discharge (ESD) protection device changes when the device is implemented in a circuit at a system level. Additionally, the operating characteristics and protection performance of an ESD-protection device may differ from device to device even if the specifications of both devices are the same. Therefore, this study aims to realize an evaluation and simulation method that can express realistic differences in the ESD-protection-performance of devices relying on transient voltage suppressor (TVS) diodes. First, we evaluated the resolution of the proposed method for measuring the protection characteristics of TVS diodes using a vector network analyzer. Second, we measured and compared four types of TVS diodes that have very similar specifications. We present the measured results for the frequency responses of the four similar TVS diodes in their operating and non-operating states. In addition, the reproducibility of the TVS-diode measurement for different printed circuit board (PCB) patterns was also examined. The results confirmed that our proposed method can express the differences between the four similar TVS diodes in terms of the attenuation of the pass frequency responses. In addition, the reproducibility of the measurement for different PCB patterns is also confirmed.