Mixed matrix composite (MMC) membranes with minimal macrovoids and defects are provided by the current invention. MMC Membranes are needed that have minimal macrovoids and defects, provide consistent and good selectivity and permeability performance, provide the mechanical strength required to withstand high membrane differential pressures, and exhibit sufficient flexibility and can easily be formed into desirable membrane forms. MMC Membranes made from a spinning dope that is stabilized with an electrostabilizing additive, particularly an acid additive, results in membranes, particularly hollow fiber membranes that have minimal macrovoids and defects. Thus, membranes of the current invention are particularly suitable for high trans-membrane pressure applications, particularly for separating oxygen/nitrogen, hydrogen/hydrocarbon, and carbon dioxide/hydrocarbon components of a stream.