Quantum dot semiconductor optical amplifiers (QDSOAs) are ideal devices for optical signal processing due to their shorter carrier recovery time and larger amplification bandwidth. With the three-level electron transition rate equations and the traveling-wave equations in QDSOAs, a segmented numerical model of the active region is established. Based on this model, the frequency response characteristics of saturated QDSOAs are obtained and the impacts of input optical power, injection current, active region length, maximum modal gain and carrier transition time on the 3 dB cutoff frequency and suppression ratio are investigated. The results show that the saturated QDSOA has a high pass filter characteristic with large bandwidth and a high 3 dB cutoff frequency. By optimizing the QDSOAs′ parameters, the more excellent properties can be obtained than the traditional buck or quantum well semiconductor optical amplifiers. These features will provide useful theoretical instructions on the designs and applications of QDSOAs at the saturated states.