In Rb:KTiOPO4 and Cs:KTiOPO4 waveguides, the dependence of the refractive index changes on the mole fraction of an admixture has been found to be of the form (Delta) ni equals Aic. In the Rb-doped case, the coefficients Ai are equal to Ax equals 0.030, Ay equals 0.026, and Az equals 0.023, whereas these are 0.16, 0.13, and 0.10, respectively, for the Cs-doped case. Also found are the effective ion diffusion coefficients: from Dz+* equals 0.11 (DOT) 10-10 cm2/c to Dz-* equals 0.17 (DOT) 10-10 cm2/c in Rb:KTiOPO4 layers at 400 degree(s)C and Dz* equals 0.56 (DOT) 10-11 cm2/c in Cs:KTiOPO4 layers at 430 degree(s)C. In the waveguides under study, the dispersion of the refractive index increments within (lambda) equals 0.44 divided by 1.15 micrometers has been shown not to occur. The synthesis regimes for the formation of single-mode channel waveguides in Z-cut KTiOPO4 have been calculated from the derived relations. Channel Rb:KTiOPO4 waveguides, single-mode at (lambda) equals 1.15 micrometers , were obtained experimentally.