LiClO4⋅3H2O has been found to be 90° phase‐matchable for ultraviolet generation at 0.2660 &mgr;m at a crystal temperature of 30.6 °C. A peak power as high as 28 MW with an average power of 2.2 W was obtained in a 1.5‐cm‐long crystal. Sellmeier’s equations and nonlinear constant of this crystal are reported. ©1996 American Institute of Physics.