Earthquakes induced during the construction of fracture reservoirs in granitoids are an important issue for the development of ultra-high-enthalpy geothermal systems. We performed axial compression experiments on granite specimens under hydrothermal conditions to evaluate this potential, simulating Quaternary granitoids at approximately 4 km depth. Our experiments were primarily conducted under a confining pressure, pore pressure, and loading velocity of 104 MPa, 39 MPa, and 0.1 μm/s, respectively, and we varied the temperature from 400 °C to 750 °C. Although failures occurred in all specimens, we observed several temperature-dependent deformation parameters. Both the apparent Young's modulus in the elastic deformation stage and the peak stress decreased with increasing temperature. Furthermore, the stress drop during failure after attaining the peak stress was slower at higher temperatures, taking almost 5 times longer at 650 °C and 750 °C than at 400 °C. We found that the fracture patterns evolved from localized to distributed and then to dissipated with increasing temperature. Well-developed fractures in quartz grains were observed at the thin-section scale, whereas fractures in feldspar grains seemed to be inconspicuous. However, SEM observations revealed that feldspar grains had actually been more fragmented, and that submicrometer feldspar particles formed within the fault gouge zone. Additionally, those feldspar fragments were sintered at temperatures above 550 °C. Sintering enhanced fracture healing during faulting, explaining the slower observed stress drop at higher temperatures and possible leading to the suppression of dynamic rupture propagations (induced earthquakes). In contrast, sintering of quartz particles in the gouge did not occur at temperatures below 750 °C, allowing for the preservation of the porous network necessary for geothermal reservoirs.