For the first time broadband sum frequency generation in ZnGeP 2 crystal has been accomplished with a compact cryogenic slab RF discharge CO laser. The spectrum of the CO laser operating in a repetitively pulsed multiline Q-switching mode consisted of ~90 emission lines in the wavelength range of 4.95-6.60 µm. Internal sum frequency generation efficiency was reached up to 8.2%. The resulted spectrum contained ~200 spectral lines in the wavelength range of 2.5-3.2 µm.