We report the demonstration of a guided‐wave nonlinear process in the material rubidium titanyl arsenate (RTA). Quasi‐phase‐matched frequency doubling of 874.5 nm light was achieved in a Cs:RTA waveguide, with a normalized conversion efficiency of 225%/W cm2. We also report phase matching characteristics for bulk periodically poled RTA. ©1996 American Institute of Physics.