Metal-organic frameworks (MOFs) films have recently emerged as highly permselective membranes yielding orders of magnitude higher gas permeance than that from the conventional membranes. However, synthesis of highly-intergrown, ultrathin MOF films on porous supports without complex support-modification has proven to be a challenge. Moreover, there is an urgent need of a generic crystallization route capable of synthesizing a wide-range of MOF structures in an intergrown, thin-film morphology. Herein, we report a novel electrophoretic nuclei assembly for crystallization of highly-intergrown thin-films (ENACT) approach, that allows synthesis of ultrathin, defect-free ZIF-8 on a wide range of unmodified supports (porous polyacrylonitrile, anodized aluminum oxide, metal foil, porous carbon and graphene). As a result, a remarkably high H2 permeance of 8.3 x10-6 mol/m2-s-Pa, and ideal gas selectivities of 7.3, 15.5, 16.2, 2655 for H2/CO2, H2/N2, H2/CH4, and H2/C3H8, respectively, are achieved from an ultrathin (500-nm-thick) ZIF-8 membrane. A high C3H6 permeance of 9.9 x10-8 mol/m2-s-Pa, and an attractive C3H6/C3H8 selectivity of 31.6 are obtained. The ENACT approach is straightforward, reproducible and can be extended to a wide-range of nanoporous crystals, and we demonstrate its application in the fabrication of intergrown ZIF-7 films.