With the consideration of cross-gain modulation (XGM) and probe-depletion (PD) effects, an analytical solution of four-wave mixing (FWM) between picosecond optical pulses in semiconductor optical amplifiers is developed based on our “splitting model.” The results indicate that the effect of PD plays an important role in the FWM process for lower pump pulse energy and smaller pump–probe frequency detuning, while the effect of XGM dominates for the pump pulse with higher energy, a shorter pulsewidth, and a larger pump–probe frequency detuning. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28: 78–82, 2001.