The invention pertains to a semi-crystalline fluoropolymer having ion exchange groups comprising recurring units derived from at least one ethylenicalty unsaturated monomer comprising at least one fluorine atom (fluorinated monomer); and a substantial amount of recurring units derived from at least one ethylenically unsaturated monomer comprising at least one ion exchange group (functional monomer), wherein the amount of unstable end groups of —COF type is of less than 0.05 mmol/kg, and the use of the stabilized fluoropolymer in fuel cells devices, a membrane and a membrane-electrode assembly.