  We discuss the existence of hierarchy of Yukawa couplings in the models with
extra spatial dimensions. The hierarchical structure is induced by the power
behavior of the cutoff dependence of the evolution equations which yield large
suppressions of couplings at the compactification scale. The values of coupling
constants at this scale can be made stable almost independently of the initial
input parameters by utilizing the infrared fixed point. We find that the Yukawa
couplings converge to the fixed points very quickly because of the enhanced
energy dependence of the suppression factor from extra dimensions as well as in
the case of large gauge couplings at high-energy scale.
