SpaceX shares shot 20% higher Monday as the company said it raised a record-breaking $85.7 billion.

The second day of gains cemented SpaceX's stellar debut on Wall Street, eclipsing the previous largest IPOs and helping make Musk the world's first trillionaire.

The stock climbed 19.7% in Monday trading to $192.8, extending Friday's 19% gain after the shares first started trading on the Nasdaq at $135.

The two-day surge sent the company's market value to more than $2.5 trillion, putting it among the six largest companies in the world: ahead of Broadcom, Saudi Aramco and Tesla and just behind Amazon.

Demand for SpaceX's shares was so strong that the banks running the sale exercised a so-called greenshoe option, in effect permission to sell extra shares when investors want more than planned.

SpaceX ended up selling nearly 639 million shares, including more than 83 million extra ones, lifting the total raised to $85.7 billion beyond the originally planned $75 billion.

Co-founded by Musk in 2002, the rocket startup has since expanded into a major satellite operator and folded in his artificial intelligence company, xAI, which includes the social media platform X, formerly Twitter.

The towering valuation rests heavily on the belief that Musk will deliver on promises worthy of science fiction, including putting humans on Mars and data centres in space using as-yet unproven technology.