A Mach-Zehnder modulator includes: a support having a principal surface, the principal surface having a first area, a second area, and a third area; a first structure including first and second semiconductor mesas disposed on the first and second areas, respectively; a second structure including a first strip-shaped semiconductor region on the second area, a second strip-shaped semiconductor region on the third area, and a first strip-shaped void and a second strip-shaped void defining the first and second strip-shaped semiconductor regions; a first electrode disposed on the first semiconductor mesa in the first area, the first strip-shaped semiconductor region of the second structure being disposed between the support and the second semiconductor mesa of the first structure in the second area, and the first and second semiconductor mesas, and the first and second strip-shaped semiconductor regions being arranged to constitute a first arm waveguide of the Mach-Zehnder modulator.