A method of making a semipermeable composite membrane comprising a discriminating layer formed insitu by interfacial polymerization is disclosed. The method provides for removal of a water immiscible solvent for a reactant in the interfacial polymerization by physical means not requiring a phase change such as a water knife, air knife, roller, or rubber blade. Composite membranes having good flux, good salt rejection, and low levels of remaining organic solvent are obtained.