Optical and electron-spin resonance (ESR) spectroscopy studies of low-temperature electron-irradiated amorphous SiO 2 were carried out to identify optical transitions of self-trapped holes (STHs). Spectroscopic analysis by means of polarized optical bleaching and thermal annealing has revealed two components comprising an absorption band around 2.2 eV: the low-energy component peaking at 2.16 eV and the high energy component at 2.60 eV. These bands are formed with similar yields in three different samples that include different chemical impurities and native defect concentrations. Based on quantitative correlations between ESR signals and optical absorption strengths, the 2.16-eV band is attributed to the two-center type STH, while the 2.60-eV band is attributed to the one-center STH. The origin of STH optical transitions is discussed based on the results of this work and recent theoretical data.