UK-based computer chip designer ARM Holdings is being sold to the American graphics chip company Nvidia for 33 billion euros.
Arm is responsible for developing the processors in most of the world's mobile phones.
The sale is still pending, and will require approval from British regulators to go ahead.
Some in the UK have called for the Government to intervene amid concerns about American control of the company.
Nvidia has promised to keep the business based in the UK, to hire more staff, and to retain ARM's brand.