Second‐harmonic generation in the proton‐exchanged LiTaO3waveguide is greatly enhanced by reducing the amount of proton exchange in fabricating the domain grating and the waveguide. To reduce the amount of proton exchange, a Ta‐SiO2mask is used for the periodic domain inversion and a SiO2mask for the proton‐exchanged waveguide. The fabricated device generates second‐harmonic blue light of 1 mW at 429 nm with the fundamental wave power of 10.3 mW. Its normalized efficiency is 1500 %/Wcm2, which is the highest value for LiTaO3waveguide devices reported to date. ©1996 American Institute of Physics.