We propose a new concept of the engineered geothermal development where reservoirs are created in ductile basement. In order to utilize ductile zone in great depth, it is necessary to develop new drilling technology. Hydrothermal brecciation were formed by explosive failure without any chemical reactions such as dissolution and precipitate, and hydrothermal brecciation could be occurred under high temperature condition involving ductile regimes in nature. Hydrothermal experiments for artificial fracturing was carried out by using visible type autoclave. Explosive failure could be occurred under relatively low pressure and high temperature difference between solid sample and injected fluid. According to hydrothermal experiments, phase transition from liquid to vapor (in other words, 'boiling') produced latent heat of evaporation, which is main reason for creating tensile fracture by thermal stress. Based on field observation and hydrothermal experiments, we could propose conceptual idea of decompression drilling technology for developing ductile rock mass.