The present invention provides, inter alia, a composition useful for producing a homogeneous, semipermeable membrane, the composition comprising a polysulfone semipermeable membrane, the polysulfone semipermeable membrane comprising a mixture of: an ultra-high-molecular-weight hydrophilic polymer, a polysulfone compound and a solvent for the polysulfone compound, and the polysulfone semipermeable membrane having a homogeneous structure such that the polysulfone semipermeable membrane has a substantially uniform structure. Another aspect of this invention discloses methods for fabricating semipermeable membranes by homogeneously mixing the composition, melting the composition, and melt-spinning the molten composition. Another aspect of the present invention includes homogeneous, melt-spun, semipermeable membranes useful for liquid separation processes, such as, but not limited to, microfiltration, ultrafiltration, dialysis, and reverse osmosis.