Synchrotron-based total ion yield and photoelectron-photoion-coincidence spectra have been applied to investigate the electronic structure and the dissociative ionization of gaseous O,S-dimethyl xanthate, CH3OC(S)SCH3, in the shallow-core S 2p region. The spectral assignment and the electronic structure are interpreted in terms of the most stable synperiplanar conformer in the C-s symmetry point group. The use of tunable synchrotron radiation allows for a selective excitation of sulfur atoms at different photon energy values, including resonance transitions and ionization around the S 2p level. The fragmentation patterns show that the title molecule is well suited as a laboratory precursor of ionic species found in the interstellar medium, especially formyl and thioformyl cations, HCO+ and HCS+, respectively.