The construction details and output characteristics of a high‐power GaAs junction laser are described. With the diode cooled to 20°K, continuous coherent optical power outputs up to 3.1 W have been obtained. This output was achieved with power efficiency of 46%. The coherent spectral output at several power levels well above threshold is shown. High resolution measurements of the spectral output place an upper limit of 310 Mc/sec upon the laser linewidth.