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With the development of transmission systems, all-optical networks need to adapt and process signals utilizing advanced modulation formats. One key element of all-optical networks is all-optical logic gates. Yet few research works on all-optical logic gates are focused on processing such signals. In this letter, all-optical XOR gates for optical quadrature phase-shift keying signals are proposed and demonstrated based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA). Error-free performance is achieved through a 40-GBaud proof-of-concept experiment with an average power penalty of 6 dB. Cross-phase modulation (XPM) effect is found to be the key limiting factor. Given the integration ability of SOA and the format transparency of FWM process, our scheme has potential for future all-optical networks. Yet the XPM effect still needs to be mitigated to achieve better performance in future works.