Switchgrass (Panicum virgatum) is a perennial warm season grass highly valued as an energy crop resource for the production of bioethanol due to its high carbohydrate content, fast growth, and ability to grow in lands that cannot support crop or food production. The recalcitrance of thelignocellulosic material can be overcome byapplying steam at high pressure and temperature during a certain amount of time, and then suddenly releasing the pressure. This opens the fibers solubilizing the hemicellulose and making the cellulose fibers more accessible to the enzymes in the following step of saccharification. Problem: Steam explosion has been demonstrated to be an efficient technology for biomass pretreatment. However, the efficiency and the selectivity of this process is highly dependent on the feedstock and conditions applied, being the temperature and residence time the two main parameters affecting the results. Therefore, the aim of the present study was to evaluate the impact of the temperature and residence time on the pretreatment of switchgrass by steam explosion in a semi-continuous pre-pilot plant able to generate between 3 and 7 kg of pretreated solid material.