We have studied the etching of siloxane/silica self-assembled monolayers in basic alcohol solutions using second harmonic generation, The kinetics of the etching process takes an unusual algebraic power law time dependence, with an exponent of 0.5, On the basis of the chemical nature of our system, we propose a surface cleavage mechanism and a surface diffusion based reaction model. We also perform Monte Carlo simulations on the system, When the solvent shell effect is considered as a geometric constraint for surface adsorption, we reproduce the anomalous power law.