ZnO thin films were sputter deposited onto oxidized silicon wafers. The film quality increased with increasing applied r.f. power. Characterization of the films was performed by measurements of the attenuation of the transverse electric TE0 optical guided mode. For an applied r.f. power of 2000 W, the deposition rate was 220 nm min−1, resulting in a mode attenuation of only 1.6 dB cm−1 for a film 0.8 μm thick. The refractive indices of the films were 99.5% (ordinary index) and 99.8% (extraordinary index) of the single-crystal values. The step coverage on etched SiO2 profiles appeared to be very smooth, which simplifies the creation of waveguiding channels. The optical behaviour of multilayered waveguides consisting of ZnO and SiO2 films was studied. A prototype of a mode coupler in such a multilayer showed the feasibility of efficient electro-optic modulation in ZnO-based waveguides.