Emission bands of the HfS radical in the region 4700–6900 cm −1 have been recorded with a resolution of 0.008 cm −1 using Fourier transform techniques. The rotational structure of the bands of the 180 H 32 S isotopomer has been analyzed and molecular parameters have been derived for the electronic states involved. The dominating part of the bands is shown to belong to theb 3 Π → a 3 Δ transition, where the[formula]andb 3 Π 1 substates are identical to the previously assignedA 1 Σ andB 1 Π states. The linkage between the triplet and singlet manifolds of HfS is established directly through the observation of the nominally forbiddena 3 Δ 1 → X 1 Σ + transition near 6620 cm −1 , as well as through additional transitions linking two common upper states[formula]andb 3 Π 1 ) withX 1 Σ + ,a 3 Δ 1 , anda 3 Δ 2 . Two further transitions connect thea 3 Δ 2 anda 3 Δ 3 substates with an additional upper state, assigned asC 1 Δ. Perturbations in theb 3 Π 2 state are observed and discussed. The term scheme of HfS is interpreted in terms of spin–orbit interaction, and electronic configurations of the electronic states of HfS are discussed.