The electronic spectrum of GeS has been studied by using ab initio based multireference configuration interaction calculations which include relativistic effective core potentials of Ge and S atoms. Potentialenergy curves of 27 Λ-S states of GeS correlating with two dissociation limits have been computed. Spectroscopic constants of bound states are computed and compared with some of the observed states such as X 1 Σ + , a 3 Σ + , b 3 Π, A 1 Π, and E 1 Σ + . The ground state of GeS is composed of two dominant configurations: ...σ 2 π 4 and ...σ 2 π 3 π* with r e ) 2.039 Å and ω e ) 549 cm -1 , which compare well with the observed values. The ground-state dissociation energy of GeS is also estimated. The observed E state is assigned to 2 1 Σ + . Effects of the spin-orbit coupling have been explored on 18 Λ-S states all of which converge with the lowest dissociation limit 3 P g (Ge) + 3 P g (S). Potential-energy curves of all 50 Ω states arising from the spinorbit interactions in these Λ-S states are computed. Transition probabilities of some dipole-allowed transitions are estimated. Transitions such as b 3 Π 0+ -X 1 Σ 0 + + and b 3 Π 1 -X 1 Σ 0 + + which are analogous to the Cameron bands of the isovalent CO are investigated. The observed a 3 Σ 1 + -X 1 Σ 0 + + transition of GeS is also studied.