The firm, which competes with rivals including Samsung Electronics Co Ltd, Micron Technology Inc and Toshiba Corp, said the plants would be completed by 2024 but did not comment on what they would make or when they would begin production.

The memory chip industry has enjoyed robust profits in recent quarters, in part due to careful capacity management by major manufacturers like Samsung and SK Hynix. Investors are closely watching new capital investment, as aggressive spending could trigger oversupply or a price war.

The new plants are part of a 46 trillion won investment plan first announced by conglomerate SK Group that controls SK Hynix last week. The plan saw the opening on Tuesday of a M14 DRAM chip plant in Icheon southeast of Seoul.

The company said the M14 plant, the largest single DRAM production plant in the world, would start making chips during the current quarter.

(Reporting by Se Young Lee; Editing by Stephen Coates)