We demonstrate a novel traveling-wave-type optical parametric generator based on 1.25-mu m pumping of HgGa2S4 that produces tunable, high-power, transform-limited proportional to 200-fs pulses in the mid-IR from 5 to 9 mu m. Output idler energies on the microjoule level are obtained with maximum conversion efficiency of 11% for the amplifier stage, which is more than two times better than the results obtained with an analogous sample of the widely spread material AgGaS2. (C) 2000 Optical Society of America