The lasing characteristics of the GaInAsP/InP narrow planar stripe lasers which were prepared by using InP epilayers as Zn‐diffusion masks in order to reduce the introduction of defects during the fabrication procedures were investigated. The narrow (?7 &mgr;m) stripe lasers showed good mode characteristics to operate in a fundamental‐transverse mode up to the output power of more than 20 mW per facet and in a single longitudinal mode in the power region. The threshold current was found to increase significantly and shifts of the lasing output towards shorter wavelength occurred as the stripe width was reduced. Remarkably wide near‐field patterns along the junction plane were obtained and far‐field patterns were found to be characterized by twin peaks in the narrow stripe lasers.