In order to develop single mode fiber optical communication, an integrated channel-substrate planar-stripe GaAs/(GaAl)As laser coupled with a two dimensional waveguide was designed and fabricated. The waveguide structure of the integrated device was designed on the base of evanescent field coupling, and the optical parameters including the refractive index and the thickness for each layer were estimated from the numerical solution of the eigenvalue equation for three and four layer slab waveguide. A reversed p-n junction was adopted for current confinement. The device was fabricated from an epitaxial wafer grown by liquid phase epitaxy on a channelled substrate with the desired layers, compositions, and carrier concentrations. Selective chemical etching and conventional device technology were nsed to fabricate the twin-laser with the two dimensional convex waveguide buried in the channel. Mode selection and amplification due to optical injection was demonstrated from the spectrum measurement, and single longitudinal mode oscillation waa achieved by suitable adjusting the synchronous pulse currents applied on the both active regions. Finally, the longitudinal mode selectivity and the relation of the active layer thickness to the mode power transfer efficiency and threshold currQat density are discussed.