The purpose of the EU funded project ThermoDriH" was the development of an alternative drilling technology for deep geothermal applications. The European project consortium made huge efforts to achieve that goal. Preliminary studies of several alternative drilling technologies revealed that high-pressure jet-assisted rotary drilling has the potential to reach the ambitious target. Comprehensive experimental studies concerning the jet cutting performance, even under high ambient pressure conditions, enabled to specify the requirements for the novel drilling system. Full-scale drilling experiments confirmed the initial assumptions and proved the superior drilling performance of the jet-assisted drilling system in hard crystalline rock compared to state-of-the-art roller cone technology. Field tests with the entire ThermoDriH system finally verified the feasibility and efficiency of the technology in the harsh real deep drilling environment.