A traveling‐wave amplifier has been fabricated from a ten‐stripe, AlGaAs phase‐locked injection laser array by antireflection coating both facets. A small‐signal gain of 18.6 dB, when corrected for optical coupling efficiency, has been observed, resulting in over 100 mW of coherent optical power output. When the signal source is a single transverse and single longitudinal mode diode laser, the far‐field radiation pattern is dominated by a single lobe with a divergence of 0.86° in the lateral plane.