"His $50 billion turned out to be $72 billion so far, he's not finished yet," Trump said, without providing details.
Trump's comments came at a groundbreaking ceremony in Wisconsin for a manufacturing facility for Foxconn, the world's largest electronics contract manufacturer, attended by Son and Foxconn Chairman Terry Gou.
Son made remarks at the event but did not reference the $72 billion figure.
SoftBank was not immediately available to comment.
In 2016, Son pledged to invest $50 billion dollars and create 50,000 jobs in the United States after meeting then President-Elect Trump.
"I couldn't have decided such a thing before this new President," Son said of that decision on Thursday.
SoftBank Group and its Vision Fund, the world's largest private equity fund which in May last year raised over $93 billion, has made many of its investments in U.S. technology firms including ride-hailing firm Uber Technologies Inc and share-office space firm WeWork.
Foxconn, which is an investor in the fund, is formally known as Hon Hai Precision Industry Co Ltd.
(Reporting by Jeff Mason; Writing by Sam Nussey; Editing by Stephen Coates and Muralikumar Anantharaman)
