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We report the metal (0–80 GPa)–semiconductor (40, 80–120 GPa)–metal (24, >120 GPa) transitions of lithium under compression, as observed through simultaneous electrical resistance and x-ray diffraction measurements. The energy gap in the 40 semiconductor quickly decreases with applied pressure, and Li reverts back to a metallic state accompanied by a structural transition to 24. The large value for 24 indicates that this re-entrant metallic phase is a so-called “poor metal.” Our results reveal a characteristic phase diagram that demonstrates the existence of a semiconductor phase between two distinct metallic phases.