The present paper is concerned with a high subcooling water jet boiling system at the stagnation point. The purpose of the investigation is to obtain a high heat flux and to reveal the high heat flux mechanism. Most of the discussion in this paper is based on experimental results and concerns the effect of subcooling, jet velocity, and stagnation pressure on critical heat flux and nucleate boiling in the transient region. The entire range of the boiling curve is divided into three heat transfer regions which may be hypothesized to exist in nucleate boiling.