Results on annealing experiments of He+ion‐implanted KNbO3planar and channel waveguides are reported. Annealing at 150 °C for several hours leads to a reduction of the waveguide attenuation constant by more than 5 dB cm−1at a wavelength of 457 nm without significant change of the profile of the mode confining barrier. A minimum waveguide attenuation constant of 1.3 dB cm−1in planar and 2.2 dB cm−1in channel waveguides at 515 nm was achieved. Second‐harmonic generation measurements in the waveguides showed that the conversion efficiency can be improved by more than a factor of 2 by the annealing process. ©1995 American Institute of Physics.