We report successful deposition of epitaxial nonlinear KTa0.52Nb0.48O3 (KTN) films on (100) GaAs substrates. A buffer layer scheme consisting of epitaxial MgO and SrTiO3 buffer layers and a Si3Ni4 encapsulation of the substrate was developed to alleviate chemical and structural incompatibilities between the GaAs substrate and KTN film at the growth temperature (∼750 °C). The structure, composition, and preliminary optical properties of the KTN films were evaluated by four-circle x-ray diffraction, Rutherford backscattering spectrometry, and prism coupled optical waveguide mode measurements, respectively. We observed sharp and distinguishable transverse electric and transverse magnetic propagating modes in the KTN films, and measured the refractive index (n0) of the film at 488 nm to be 2.275 which is close to the bulk value of 2.35, all of which indicates a high structural and optical film quality. © 1998 American Institute of Physics.