Some of the world’s most prominent names in technology are pledging to pour as much as half a trillion dollars into building artificial-intelligence infrastructure in the U.S., in the latest high-profile initiative timed with the start of the Trump administration. The joint venture, known as Stargate, is led by the ChatGPT maker OpenAI and the global tech investor SoftBank Group . It will build data centers for OpenAI. The database company Oracle and MGX, an investor backed by the United Arab Emirates, are also equity partners in the venture.

The companies are committing $100 billion to the venture and plan to invest up to $500 billion over the next four years. The plans, key elements of which remain vague, were announced Tuesday at a White House ceremony with President Trump.

The $100 billion sum includes projects that the companies already announced and initiated under the Biden administration, people familiar with the matter said.

The total figure—if realized—would be large even by Silicon Valley standards and underscores the extent to which tech companies and government officials are betting on AI as the future of the American economy . It also shows how much tech executives want to broadcast their enthusiasm at the start of the new administration.

OpenAI Chief Executive Officer Sam Altman , SoftBank CEO Masayoshi Son and Oracle Chairman and Chief Technology Officer Larry Ellison went to the White House for the announcement Tuesday, the second day of the second Trump administration.

Stargate’s first data center will be in Texas. The site, which started construction last year, will be operated by Oracle and used by OpenAI, a person familiar with the project said.

The companies didn’t disclose how much cash each partner would contribute. OpenAI has raised billions of dollars, but still loses money. Oracle has about $11 billion in cash and marketable securities but more in debt. SoftBank has roughly $30 billion of cash on hand.

OpenAI said it would operate the venture, while SoftBank will finance it. Stargate will have a separate board of directors and hire a new CEO. SoftBank’s Son will be chairman.

Stargate plans to bring on additional equity investors, people familiar with the matter said. SoftBank is also planning to raise debt from third parties to pay for Stargate’s projects.

Microsoft , OpenAI’s largest investor and compute provider, as well as the chip makers Arm Holdings and Nvidia , were named “technology partners” in Stargate, meaning they will be involved in creating Stargate’s infrastructure.

In a separate announcement, Microsoft said it would continue to be the primary provider of cloud computing for OpenAI but would also allow the startup to use other providers on a case-by-base basis.

OpenAI kicked off the modern AI boom when it released ChatGPT in 2022. The chatbot’s popularity forced tech companies to redraw their product plans and earmark billions of dollars to build AI systems and tools. Most of that money goes toward building data centers to hold the racks of the pricey and powerful chips that power AI systems.

Goldman Sachs has estimated that companies, including the American tech giants, would spend an estimated $1 trillion on capital expenditures in coming years. That would include large outlays in data centers, chips and the power grid.

Altman has been meeting with investors from the Middle East to pitch them on his own tech initiative to expand the world’s chip-making capacity. Such an effort might require several trillions of dollars, The Wall Street Journal previously reported.

Write to Deepa Seetharaman at deepa.seetharaman@wsj.com and Tom Dotan at tom.dotan@wsj.com