The controversy escalated on several fronts on Tuesday as allegations emerged that Huang's relationship with Alice Huang aided at least $US7.5 billion ($A10.9 billion) in Nvidia chip shipments to China and that US Secretary of State Marco Rubio had previously briefed President Donald Trump on the affair.
Senate Democratic Leader Chuck Schumer demanded answers from the administration and tighter curbs on chip exports to China, while the company's independent directors hired outside counsel to investigate.
Republican US Senator Kevin Cramer from the Senate Banking Committee called on Huang to step down.
"The potential for extortion is so tremendous that something as sensitive as Nvidia chips, I just think he's got to go," Cramer told Politico on Tuesday.
The allegations have turned Huang's personal conduct into a broader risk for Nvidia, raising questions about the company's governance and its dependence on the boss who has led it for more than three decades and built it into the dominant supplier of AI chips.
He owns about 3.6 per cent of the company - but does not have majority voting control - and runs an unusually flat organisation in which dozens of executives report directly to him.
The FBI is separately examining whether 63-year-old Huang was targeted by a foreign intelligence operation.
Huang has told employees he was unfaithful to his wife, but provided no details about the relationship. China's foreign ministry has said the spy accusations are "groundless".
Huang apologised to top executives at a meeting on Monday before pivoting to business and was back holding meetings at Nvidia's headquarters on Tuesday, CNBC reported.
Nvidia has said its board has no reason to believe US national security or company secrets were compromised and that Huang has committed to co-operating with the internal review.
The board has retained Joon Kim, a Wachtell Lipton partner and former acting US Attorney for the Southern District of New York, whose practice includes internal investigations and white-collar defence, to lead the probe.
Nvidia's stock, which had been nearly flat this year before news of the affair broke, has fallen 9.5 per cent since then. The shares have lagged the broader market on investor unease over whether massive spending on AI will deliver adequate returns.
The New York Times reported on Tuesday that Rubio had briefed Trump aboard Air Force One en route to China in May about US intelligence indicating Huang was involved with a woman believed to be a Chinese spy.
The briefing marked at least the second time in seven months that Trump had been told about the intelligence, the Times reported.
Trump said on Monday he had spoken with Huang and asked whether he knew the woman was a spy. Trump said Huang told him he had "absolutely no idea" and that he believed the Nvidia boss.
Trump also said he had not known about the alleged ties when Huang accompanied him to China in May.
Schumer said on Tuesday that Congress must have a full accounting of Trump's defence of Huang and called on lawmakers to quickly approve new restrictions on US chip exports to China.
"He's supposed to protect America, not China, not his friends," Schumer said, accusing Trump of failing to address foreign espionage in the American technology industry.
