Thermally rearranged polybenzoxazole (TR-PBO) hollow fiber membranes were fabricated from a poly (amic acid) (HPAAc) precursor through a non-solvent induced phase separation technique (NIPS). All the major fabrication conditions (e.g. dope composition, the use of additional inorganic salt, dope and bore flow rates, and coagulation bath temperature) were systematically evaluated and optimized, in order to produce defect-free hollow fiber membranes with an ultra-thin skin layer. The hollow fiber membranes fabricated with the optimized spinning conditions exhibited superior pure gas permeation behavior (CO2 permeance of 2500 GPU and CO2/N-2 ideal selectivity of 16). Slow beam positron annihilation lifetime spectroscopy (slow beam PALs) measurements revealed that such an exceptional separation performance was mainly attributed to the ideal cavity radius (3.584 angstrom) and ultra-thin skin layer thickness (193 nm) obtained using the optimal fabrication conditions. In addition, mixed-gas permeation tests were also performed to demonstrate the feasibility of using such membranes for post-combustion CO2 capture. (C) 2015 Elsevier B.V. All rights reserved.