Mass spectrometry (MS) is an established analytical technique to analyze evolved gas in thermogravimetry (TG). In this study, for the first time a novel SPI-MS technique using an electron beam pumped VUV excimer lamp as photon source (lambda = 126 nm) was employed in conjunction with thermogravimetry. The coupling was achieved with an improved heated interface and adjacent transfer capillary between TG and ion source of a quadrupole mass spectrometer. The feasibility of this approach was proven by investigating semivolatile substances such as long-chain alkanes (heptadecane C17H36), polymers, e.g., polystyrene, polycarbonate, and acrylonitrile-butadiene-styrene, polymer mixtures and blends. Mass spectra with almost no fragmentation were obtained, and quantification of selected substances could be achieved. Polymer mixtures could be distinguished by their SPI mass spectra, and the effect of premixing of polymers has been accessed. Its unique attributes render the TA-SPI-MS method a promising new tool for quantitative and qualitative evaluation of complex organic thermal degradation products.