Planar waveguides inz‐cut LiTaO3have been fabricated by ion exchange in pyrophosphoric acid. The dependence of the refractive index change and waveguide depth on the ion‐exchange time and temperature, and the anneal time and temperature has been investigated. In addition, waveguide transmission and inversion depths have been measured. The ion exchange temperature and duration were varied between 230 and 293 °C and 15 and 90 min, respectively. The anneal temperature and duration were varied between 300 and 594 °C, and 16 and 840 s, respectively. Under certain conditions the depth of the waveguide was shown to have a simple dependence on the processing conditions. The minimum waveguide coupling and propagation loss was measured to be 0.4 dB. Inversion was observed for anneals of 180 s and temperatures of 525–594 °C. ©1995 American Institute of Physics.