Tech stocks rebounded from a recent slump driven by fears of an AI bubble, although concerns are growing about industry giants’ off-balance-sheet debt.

Shares in chipmakers Samsung and TSMC in particular saw big gains from comparative lows, as investors bet that semiconductor demand would continue; tech-heavy benchmarks in South Korea, Taiwan, and China all rose.

But according to Nikkei, financial statements from Alphabet, Amazon, Meta, Microsoft, and Oracle revealed hidden debt of $1.65 trillion — up eightfold in four years — as they race to build data centers. Though the firms expect future earnings to exceed those debts, the market has “begun to show concern,” the outlet reported; Morgan Stanley and Moody’s both also highlighted the issue in reports.