(Bloomberg) — A co-founder of SenseTime Group Inc. lost almost half of his fortune after shares of the artificial intelligence giant plummeted 47% on Thursday.

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Tang Xiao’ou, a Massachusetts Institute of Technology graduate and information engineering professor at the Chinese University of Hong Kong, has a 21% stake in the company. His net worth plunged by about $2.4 billion to $2.8 billion, based on the closing share price, dropping him off a list of the world’s 500 richest people, according to the Bloomberg Billionaires Index.

The fall of SenseTime occurred after the lock-up period on a portion of shares held by cornerstone investors and stakeholders expired a day earlier. Some executives, including Chief Executive Officer Xu Li, pledged to extend the lock-up of their shares until Dec. 29.

The tech company completed a Hong Kong listing in December despite US sanctions, and surged as much as 23% on debut. Thursday’s slump dragged the stock below the initial public offering price for the first time.

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SenseTime’s technology has been deployed in a range of areas, including assisting police in China, providing product placements in films and creating an augmented reality scene in a mobile game by Tencent Holdings Ltd.

SenseTime reported revenue of 4.7 billion yuan ($702 million) and a loss of 6.9 billion yuan last year.

(Updates shares, loss and net worth in first two paragraphs)

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This story originally Appeared on Yahoo