Noninverted wavelength conversion has been demonstrated using Fabry-Perot semiconductor optical amplifiers (FP-SOAs), and its mechanism is theoretically analyzed. The noninverted behavior is dominated by the shift of gain spectrum in the FP-SOA. Increasing the input optical power suppresses the spontaneous emission and drives the gain spectrum toward the longer wavelength side due to the enhancement of carrier-photon interaction. The performance of wavelength converters is improved owing to the resonant effect at the probe wavelength and this type of converter provides an effective approach for wavelength conversion in the future broadband networks.