We present the first photoemission study of mixed valence Yb 3Si 5. A monophasic, polycrystalline sample has been studied with synchrotron radiation in the range 65-450 eV and with MgK α radiation. The wide hv range allows the surface sensitivity to be changed strongly due to the energy dependence of escape depth. The ratio of the intensities from Yb 2+ and Yb 3+ is higher when the surface sensitivity increases; this trend can be fitted accurately with a simple model which gives valence ≈ 2.6 at room temperature in the bulk and at least one surface layer with divalent Yb. The fitting gives also the energy dependent escape depth. We give also the shifts of the Yb bulk and surface f states upon Yb 3Si 5 formation which explain the different valence in the bulk and at the surface. Si2p photoemission shows the effect of inequivalent Si sites in Yb 3Si 5.