We show the existence of an intrinsic generation mechanism of OH groups in synthetic dry silica upon thermal treatments. Samples are treated for ∼160 h at 390 °C in He at 2.7 or 180 bar, and the growth of the OH IR absorption band at 3670 cm-1 is observed. An OH concentration of ∼1018 cm-3 is estimated. Possible contributions of reactions with molecules absorbed from the atmosphere are excluded. Reactions with H2O already contained in the samples are rejected by IR measurements. The observed OH generation is attributed to the reaction of network sites with H2 already present in the material. Possible reaction paths are examined.