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Herein, we present a study investigating the reaction conditions to wet etch monocrystalline silicon in the subcritical region of water, specifically from 200 to 300 °C. In the subcritical region there is a departure of thermodynamic, transport, and chemical properties from normal conditions. This has the potential to affect the reaction paths for the dissolution of silicon, by modifying the local concentration of reactants and products, by altering the relative activation energy of different reactions, or by changing the polarity of the water. Furthermore, our methodology uses concentrations of etching agent markedly lower than previous works (our reactions were conducted at [KOH] = 0.03–0.7%/wt). The results of the study suggest that dilute etchant solutions at high temperatures can produce results comparable to those reported at atmospheric conditions using higher concentrations of etchants. Based on the results obtained, the main key factors in the etch rates were crystallographic orientation of the wafer, composition of the etching solution, and temperature.