A twin-mesa GaAs-(AlGa) As laser integrated with a passive waveguide is described. It is characterized by amplification with electro-optical injection and mode locking. The laser can be oscillated in a single longitudinal and fundamental transverse mode with a △λ about 1-1.6A by adjusting the synchronous pulse driving currents of both mesas A and B at slightly above threshold. When the ambient temperature is changed abont 1~2℃, a single mode operation can be still obtained.