We investigate left-handed (LH) travelling-wave field-effect transistors (TWFETs) to observe the reverse Doppler effect. Due to the nonlinearity, a TWFET can support shock fronts that can reflect incoming waves. By introducing the composite right/left-handed line structure to a TWFET, it enables to support LH waves. Because the shock front functions as a moving reflection wall to the incoming LH waves, we can expect the reverse Doppler effect to cause in an LH TWFET. After explaining the structure and fundamental properties, we report the reverse Doppler effect observed experimentally in the devise.