A Mach-Zehnder (MZ) modulator made of semiconductor material and a method to drive the MZ-modulator are disclosed. The MZ-modulator includes a pair of arms to vary the phase of the optical beam propagating therein. One of the arms further provides the phase presetter that varies the phase of the optical beam by π. The arms are driven by modulation signals complementary to each other but with the DC bias equal to each other.