Absolute concentrations of H atoms and OH radicals were measured to determine the product branching ratios for the reactions SiH3 + O2 → SiH2O + OH (1b) and SiH3 + O2 → SiH2O2 + H (1c) by using laser-induced fluorescence (LIF) techniques. The intensity of the VUV-LIF signal of H atoms at Lyman a wavelength was calibrated against the absolute concentration determined by the simultaneous measurement of the Lyman α resonant absorption. The calibration for the UV-LIF signal intensity of OH radicals has been performed by the simultaneous measurements of the VUV-LIF of H atoms and UV-LIF of OH produced in the O(1D) + H2 → OH + H reaction system: since the reaction of O(1D) + H2 produces equal amounts of H and OH, the absolute concentration of OH could be known from the H-atom concentration derived from the VUV-LIF intensity of H atoms. It was found that vibrationally excited OH in v″=1 was also produced by reaction 1b with a ratio of [OH(v″=1)]/[OH(v″=0)] = 0.49 ± 0.08. The yields of H and OH in the SiH3 + O2 reaction were derived from the measured absolute concentrations of H and OH combined with the absolute concentrations of SiH3 determined by the time-resolved mass spectrometry. The branching ratios of 0.25 and 0.65 for reactions 1b and 1c, respectively, were obtained on the basis of kinetic simulations for the yields of H and OH.