Hot compressed liquid water was used to treat switchgrass in a method called hydrothermolysis to disrupt lignin, dissolve hemicellulose, and increase accessibility of cellulose to cellulase. Three temperatures (190, 200, and 210°C) and hold times (10, 15, and 20min) were tested. Switchgrass treated at 190°C for 10min had the greatest xylan recovery in the prehydrolyzate. Less than 0.65g/L glucose were released into the prehydrolyzate for all pretreatment conditions, indicating most glucose was retained as cellulose in the solid substrate. 5-Hydroxymethylfurfural (HMF) and furfural formation in the prehydrolyzate were found to be less than 1g/L for all treatments. The highest concentration of ethanol, 16.8g/L (72% of theoretical), was produced from switchgrass pretreated at 210°C and 15min using simultaneous saccharification and fermentation (SSF) at 45°C with the thermotolerant yeast Kluyveromyces marxianus IMB4 and 15FPU cellulase/g glucan.