Dielectric mirrors with an oxide coating for a parametric light generator based on a ZnGeP2 single crystal were fabricated. The threshold values of laser-induced breakdown of dielectric mirrors made for single-pass (no. 1) and multi-pass (no. 2) resonators (3.5 ± 0.1 and 3.9 ± 0.1 J/cm2, respectively) are determined. Based on the obtained data, the mirrors were tested in the OPO system based on the ZnGeP2 single crystal. The maximum generation efficiency achieved in the experiment was ~54% when using mirror no. 1 and 50% when using mirror no. 2. In this case, the average power of the generated OPO radiation was 7.7 and 3.7 W when using mirror no. 1 and mirrors no. 2, respectively. The possibility of creating a dielectric mirror with high radiation strength operating in the range of 3.5–5 μm on a sapphire substrate is shown.