Single-frequency lasing of quantum-cascade lasers with a distributed Bragg reflector formed by the focused ion beam milling technique in the layers of the upper cladding of the waveguide is demonstrated. The active region In0.53Ga0.47As/Al0.48In0.52As is formed based on the scheme with two-phonon lower energy level depopulation in the cascade. Single-frequency lasing at a temperature of 280 K corresponded to a radiation wavelength of 7.74 μm; the side mode suppression ratio (SMSR) was 24 dB.