Our X-ray diffraction measurements reveal that Mn₂O₃ undergoes a phase transition to the CaIrO₃ type, which is proposed for the post-perovskite in MgSiO₃, at 27–38 GPa and 300 K, bypassing the other phase transitions observed in sesquioxides. Small distortions in the polyhedra after the transition indicate that the Jahn-Teller effect, which is strong at ambient conditions, is suppressed during the transition. The CaIrO₃-type phase exhibits strong preferred orientation of the (010) plane perpendicular to the loading axis before annealing whereas preferred orientation of the (100) and (110) planes was observed after annealing. The pre-annealing texture may result from either the deformation under strong differential stresses or the phase transition. The post-annealing texture may be related to either lower differential stresses or thermal annealing. Our result shows that the texture of the CaIrO₃ type can be sensitive to phase transition and annealing as well as differential stresses.