A model of integrated twin-guide semiconductor optical amplifier optical switch (ITG-SOA-Switch) is proposed. Comparison analyses with semiconductor optical amplifier (SOA) reveals that because of the combination of several physical effects by ITG-SOA-Switch, only a small increase of input power around 3 dB saturation point can cause a big decrease of gain. Theoretical analyes and the simulation results of 10Gbit/s wavelength conversion indicate that the extinction ratio of output converted signal of ITG-SOA-Switch can be greatly improved compared with that of input pump signal in a moderate pump power range.