We study the pressure-induced phase transition of the layered GeS structure using a constant-pressure ab initio technique. For the first time, we predict a gradual phase transition to a Cmcm structure with the application of hydrostatic pressure. The high-pressure phase is still a layered structure, consisting of rocksaltlike bilayers, but it has an unusual fivefold coordination. The transition is due to the significant decrease of second neighbor distances. We also find the metallization of GeS prior to transforming into the Cmcm phase.