The process of the resistance generation in a YBCO thin film during the S/N transition used in resistive type fault current limiters has not been clarified completely. During the process, a thin film may be broken by overheat. Understanding the process of the resistance generation would lead to prevent thin films from this burnout. In this paper, the voltage distribution of a YBCO thin film during the S/N transition is measured by probes arranged 2 dimensionally on a thin film to understand how the normal transition area on a YBCO thin film expand. The voltage probes are placed in a matrix of 3 times 10 on a 30-by-210 millimeter YBCO thin film. A sinusoidal wave current whose amplitude is several hundreds ampere flows into the thin film connected with a parallel resistance. It is observed from these measurements that a narrow normal conducting state band vertical to the current appears first, and this band expands along the current. The critical current of the area on the thin film where the normal conducting state band appears first is the lowest along the thin film. This band is considered to have a great influence on the resistance generation of the YBCO thin film.