US President Donald Trump has blocked a planned takeover of chipmaker Qualcomm by Singapore-based rival Broadcom on grounds of national security.
His order cited "credible evidence" that the proposed $140 billion deal "threatens to impair the national security of the US".
There were concerns the takeover could have led to China pulling ahead in the development of 5G wireless technology.
The deal would have been the biggest technology sector takeover on record.
A takeover of Qualcomm by Broadcom would have created the world's third-largest maker of microchips, behind Intel and Samsung.