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Injecting spins from ferromagnetic metals into semiconductors efficiently is a crucial step towards the seamless integration of charge- and spin-information processing in a single device. However, efficient spin injection into semiconductors has remained an elusive challenge due to the extremely low injection efficiencies originating from impedance mismatch, or technological challenges due to stability and cost issues. In Co/MoS₂, by making use of the strongly out-of-equilibrium character of the injected spins, we demonstrate a highly-efficient spin injection from a ferromagnet (Co) into a semiconductor (MoS₂), thus overcoming the crippling problem of impedance mismatch. Astonishingly, we measure a giant spin current that is orders of magnitude larger than typical injected spin current densities using currently available techniques. Our result demonstrates that technologically relevant spin currents can be driven by ultralow-intensity laser pulses, finally enabling ultrashort spin-current pulses to be a technologically viable information carrier for terahertz spintronics. Nature Physics, DOI:10.1038/s41567-018-0406-3 (2019).