The strain‐induced periodical domain inversion in KTiOPO4(KTP) has been demonstratedinsituby means of the nonlinear light diffraction. The temperature of 730 °C was found to be the starting point of the opposite sign domains growth under the heating of −ZKTP substrate (rate 70 °C/s) with the periodical SiO2mask. The depth of the fabricated domain‐reversed structure of the 5.5 &mgr;m period was measured to be 4.5 &mgr;m. ©1996 American Institute of Physics.