In this paper ∼16 μm-emitting multimode InP-related quantum cascade lasers are presented with the maximum operating temperature 373 K, peak and average optical power equal to 720 mW and 4.8 mW at 303 K, respectively, and the characteristic temperature (T₀) 272 K. Two types of the lasers were fabricated and characterized: the lasers with a SiO₂ layer left untouched in the area of the metal-free window on top of the ridge, and the lasers with the SiO₂ layer removed from the metal-free window area. Dual-wavelength operation was obtained, at λ ∼ 15.6 μm (641 cm⁻¹) and at λ ∼ 16.6 μm (602 cm⁻¹) for lasers with SiO₂ removed, while within the emission spectrum of the lasers with SiO₂ left untouched only the former lasing peak was present. The parameters of these devices like threshold current, optical power and emission wavelength are compared. Lasers without the SiO₂ layer showed ∼15% lower threshold current than these ones with the SiO₂ layer. The optical powers for lasers without SiO₂ layer were almost twice higher than for the lasers with the SiO₂ layer on the top of the ridge.