Strongly confining waveguides were fabricated in LiTaO3at high temperature (540–610 °C) by short‐time (≤6 s) rapid thermal annealing. Single‐step photolithography is able to accomplish the simultaneous fabrication of a waveguide and a periodically domain‐inverted structure for second‐order quasiphase‐matching blue‐light generation. A measured normalized conversion efficiency of 7%/W cm2for a physical length of 0.55 mm in a planar quasiphase‐matching waveguide showed that this single‐step process can lead to high conversion efficiency in channel waveguides. ©1996 American Institute of Physics.