Polymeric porous membranes with excellent thermal (Td higher than 500 °C) and solvent resistance were prepared. The membranes were based on three high-performance polymers (polyoxindolebiphenylene, polytriazole and polybenzimidazole), functionalized with alkyne side groups. The functionalization enabled the polymer crosslinking by a fast and simple wet-state thermal process in hot glycerol. The effect of crosslinking time and temperature was evaluated. The obtained membranes were characterized by spectroscopy and thermal analysis. The membrane morphology was investigated by electron microscopy. The liquid separation performance of the crosslinked membranes was evaluated in several organic solvents. The stability in filtration experiments was demonstrated in dimethylformamide at temperatures up to 140 °C. The solvent resistance in various solvents was confirmed in long-term tests (up to 21 days) at room temperature.