SK Hynix’s planned U.S. listing this week will test the AI-fueled chip rally, offering investors a chance to buy a memory chip maker not named Micron Technology—or to stay away from a group that may have come too far, too fast. U.S. investors can get exposure to the country with the iShares MSCI Korea exchange-traded fund, but buying Samsung Electronics or SK Hynix individually has been almost impossible.