High-resolution linearly polarized S K-edge X-ray absorption spectra for charge-transfer salts, lambda-(BETS)(2)GaCl4 and beta-(BEDT-TTF)(2)PF6 (BETS: bis(ethylenedithio)tetraselenafulvalene; BEDT-TTF: bis(ethylenedithiolo)tetrathiafulvalene) have been measured using undulator radiation. For both the compounds, weak bands below the most intense sigma* transition are found. These characteristic bands are absent for the corresponding neutral compounds, BETS and BEDT-TTF. They are assigned to the transition to the highest occupied molecular orbital based on linear polarization dependence. These bands are proposed as a novel probe for determination of the hole concentration in the charge-transfer salts containing BETS and BEDT-TTF analogues.