Almost all the gains in U.S. technology stocks have now been wiped out this year. Across the Pacific, the rout has been going on for some time already.

Korea’s benchmark Kospi Composite Index fell into a bear market Thursday, dragged down by Samsung Electronics and memory-chip maker SK Hynix. The two companies, which together account for around a quarter of the index, have fallen around 30% from their peaks late last year, despite both continuing to report record earnings. SK Hynix said Thursday its operating profit last quarter...