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We report significant improvements in threshold current density and maximum operating temperature in continuous wave (CW) operation of interband cascade lasers (ICLs) near 5 μm. The uncoated ICLs were demonstrated at room temperature with a threshold current density of 343.8 A/cm2 and an output power of 31 mW/facet at 25 °C in CW mode. Different ICLs made from the same wafer were compared to study the impact of device dimensions on performance. The threshold current density of 331 A/cm2 achieved from a facet-uncoated 5 mm-long device at 25 °C is the lowest among all previously reported room temperature CW ICLs with emission wavelengths longer than 4 μm. Compared to the previous record of 480 A/cm2 at 4.75 μm for a facet-coated 4-mm-long ICL at 25 °C, this value of 331 A/cm2 is reduced by 31%, representing a substantial improvement. Benefited from improved device fabrication and enhanced thermal dissipation, the maximum CW operating temperature of the device reached 66 °C, which is the highest ever reported for ICLs with similar emission wavelengths.