We performed an x-ray spectroscopic study combining resonant x-ray emission spectroscopy (RXES) and photoelectron spectroscopy on the superconducting ternary silicide YbGa_<1.15>Si_<0.85> and nonsuperconducting ternary germanide YbGa_xGe_<2-x> (x = 1.0 and 1.1). The Yb valence for all three compounds is found to be about 2.3. In YbGa_<1.15>Si_<0.85> no temperature dependence of the Yb valence is observed in the RXES spectra in the temperature range of 7-300 K, while the valence shows a drastic increase under pressure from the Yb^<2+> state partially including itinerant electrons to the localized Yb^<3+> state. Differences are observed in the valence-band spectra of the photoelectron spectroscopy between YbGa_<1.15>Si_<0.85> and YbGa_xGe_<2-x>, which may be attributed to the difference of crystal structure. We conclude that both the crystal structure of the planar GaSi layer in YbGa_<1.15>Si_<0.85> and the resultant electronic structure may have a crucial role in the occurrence of superconductivity.