Gas phase species generated by thermal decomposition of disilane were studied using resonance enhanced multiphoton ionization at disilane pressures ranging from 1-10 Torr and temperatures ranging from 300-1000 K. Atomic Si, mass 23, was observed at 487.9, 417.7, and 416.2 nm. A mass-30 signal was not observed between 494-515 nm. Masses 2, 32, and 60 were observed using multiphonon ionization and were photoionization fragments from higher silanes and silenes. Thermal decomposition reactions were the main source of atomic Si for the mass-28 signal, although ionization of SiH2 and higher silanes followed by fragmentation may have contributed some of the mass-28 signal.