Stimulated emission pumping spectra of the A ¹B₁- X ¹A_{_1} transition of SiH₂ radical were observed in order to obtain information about the a ³B₁ state through the spin-orbit interaction. The vibrational level structure of the X state, which is the basis of the present observation of the triplet state, was well described with a polyad structure, in which both the 1ν₁:2ν₂ Fermi and the 2ν₁:2ν₃ Darling-Dennison anharmonic resonances were considered. In the P=10 polyad, four sets of spin-orbit perturbations were observed for the first time. The triplet state observed at about 9640 cm^-1 from the (000) level of the X state was tentatively assigned to be the a ³B₁ (030) level. An analysis of the spin-orbit interaction showed that the interaction energies of the spin-orbit coupling are 0.73-3.13 cm^-1. This value is rather smaller than that expected based on the comparison with CH₂. This is considered to be due to poor overlap between the vibrational wave functions in the a and the X state.