Fabrication and characteristics of mesa-stripe-geometry double-heterostructure injection lasers are described. Two types of lasers have been prepared: 1) low mesa-type lasers in which mesa etching is stopped just above the active layer and 2) high mesa-type lasers in which mesa etching is effected up to the first epitaxial layer (n-GaAlAs). The stripe widths of these lasers can be narrowed below 30 μm without an appreciable increase of the threshold current density. As a result, very low current operation has been realized. The thermal resistances of these lasers are nearly as low as those of stripe-geometry lasers. This property along with the low threshold current density renders it easy to operate diodes continuously at and above room temperature. Near-single-mode operation has been observed in low mesa-type lasers. The laser emissions display TE polarization in most cases; however, diodes with thick active layers have often been observed to show TM polarization.