The isotypic trielborates c-Al5B12O25(OH), c-Al1.7Ga3.3B12O25(OH), and c-Ga4InB12O25(OH) were synthesized under high-pressure/high-temperature conditions of ≥12 GPa and ≥1100 °C. The three cubic compounds crystallize in the space group Fmurn:x-wiley:14341948:media:ejic202001136:ejic202001136-math-0001 m with Z=4 and a=10.8226(5), 10.9258(5), and 11.176(2) Å for c-Al5B12O25(OH), c-Al1.7Ga3.3B12O25(OH), and c-Ga4InB12O25(OH), respectively. The crystal structures of all three compounds were determined by single-crystal X-ray diffraction revealing disordered cubic structures composed of MO6 octahedra (M=Al, Al/Ga, Ga, In) and BO4 tetrahedra. Single-crystal Raman and IR spectroscopic data further characterize the compounds, and the latter confirms the presence of hydroxyl groups.