A defect-free membrane with a very high gas permeance is greatly attractive to both academia and industry. Thin film composite (TFC) membranes are promising candidates. However, it is always challenging to have a reproducible and up-scalable method to fulfill the needs. Herein, we report a novel and straightforward strategy to fabricate a high-performance hollow fiber composite membrane using a crosslinked polydimethylsiloxane (PDMS) with a high inherent viscosity obtained from a novel post-crosslinking method. The evolution of inherent viscosity with various cross-linking conditions and substrate morphology from different spinning conditions have been investigated. The resultant defect-free composite membrane shows excellent O-2 and CO2 permeances higher than 1000 and 5000 GPU, respectively; while the corresponding selectivities of O-2/N-2 and CO2/N-2 are about 2 and 11, respectively. The newly developed methods may provide useful insights to fabricate nextgeneration high-performance composite membranes for gas separation.