GaAs injection lasers were prepared by an epitaxial solution growth method and their properties compared with those of diffused junctions. The optical gain factor β was up to a factor of 7 higher for the epitaxial diodes at 300°K. This resulted in threshold current densities as low as 26 000 A/cm2 (3.8×10-3 cm length) at 300°K. At 77°K, gain factor and loss numbers were similar for the two laser types. The spontaneous line-width of the epitaxial lasers was unusually large (∼300 Å at 77°K) and increased with decreasing junction voltage. The internal quantum efficiency of epitaxial diodes drops from 100% at 4.2°K to 40% at 300°K. The vertical beam spread was found to be between 20°-30°half-width at 77°K as well as at 300°K. Diffused diodes frequently show a delay between the current pulse and the stimulated emission of up to 30 nsec, dependent on the current value at higher temperatures. No such delay was observed in epitaxial lasers. © 1967 The American Institute of Physics.