Cellulose is one of the largest renewable resources in nature, which has not been completely exploited. It is present in a lignocellulosic complex in agro-industrial residues such as sugarcane bagasse. Fermentable sugars, which can be further fermented to bioethanol, can be obtained by hydrolyzing these lignocellulosic raw materials. The clean and rapid method of sub/supercritical water hydrolysis has been proven technically feasible for this purpose. Most information available in literature on that subject was obtained using batch or continuous equipments; therefore there is a lack of information on the semi-batch process. The objective of this work was to assemble a semi-batch equipment for sub/supercritical hydrolysis using water as reaction medium with possible addition of CO2 as catalyzer. The system was designed to work with pressures up to 40 MPa and temperatures up to 400 °C; it consists of a water pump, a CO2 pump, a heating coil, a mixer, a 50 mL reactor, where the raw material is fed, inserted in an electric heating jacket, a pressure drop valve, another mixer for CO2 injection for quenching the reaction and a collector flask. The system was validated using cellulose as reference material at the subcritical conditions of 184 °C, 197 °C and 209 °C for 68 min and under 20 MPa. The optimal condition was applied to hydrolysis of sugarcane bagasse. Total reducing sugars were determined using a colorimetric method. At 184 °C there was no reducing sugars recovered. At 197 °C and 209 °C the reducing sugars recovery rate increased up to a maximum and then decreased until there was no reducing sugars detected anymore. The total reducing sugars recovered at 209 °C was higher than at 197 °C and the process at 209 °C was faster. Therefore, sugarcane bagasse hydrolysis was performed at 209 °C.