We demonstrate an optical parametric oscillator (OPO) based on GaAs. The OPO utilized an all-epitaxially-grown orientation-patterned GaAs (OP-GaAs) crystal, 0.5-mm-thick, 5-mm-wide, and 11-mm-long, with a domain reversal period of 61.2 μm. By tuning either the near-IR pump wavelength between 1.75 and 2 μm, or the temperature of the GaAs crystal, the mid-IR output tuned between 2 and 11 μm, limited only by the spectral range of the OPO mirrors. The pump threshold of the singly-resonant OPO was 16 μJ for the 6-ns pump pulses, and the photon conversion slope efficiency reached 54%. Also, we show experimentally the possibility of pump-polarization-independent frequency conversion in GaAs.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.