Numerous pretreatment strategies that have been developed to degrade or remove lignin from lignocellulosic residues to promote the production of sugars by enzymatic saccharification have been described in the literature. Among them, alkaline hydrogen peroxide (AHP) at atmospheric pressure has been described as an efficient method. In this work, a new pretreatment that combines in one stage a process at high pressure (10-30 bar) and alkaline hydrogen peroxide (HPAHP) has been developed. For experiments performed at atmospheric pressure, the maximum hydrolysis yield (72.91 ± 5.93%) was obtained at 7.5% w/v H2O2, with a reaction time of 2 h. With the proposed high-pressure method, a maximum hydrolysis yield of 98.50 ± 6.28% was reached with a reduced peroxide concentration of 3% w/v, a reaction time of 30 min, and a pressure of 30 bar. These HPAHP pretreatment conditions were optimized using a statistical design of experiments. Results showed that the operation variables with the most significant effects on global yield were temperature and peroxide concentration. The response surface model predicts that the optimized conditions for global yield are 3% w/v H2O2, 30 min, 28 bar, and 90 °C. In conclusion, HPAHP pretreatment could be an interesting option for the industrial delignification of rice husk or other lignocellulosic biomass.