SK Biopharmaceuticals shares plummeted as much as 10 percent Monday as almost 5 million shares were released after a lock-up period.

Shares in the pharmaceutical company declined 8.58 percent to close at 154,500 won ($142) after plunging as much as 10 percet during trade as the last batch of shares that were locked in after the initial public offering were freed to the market. The benchmark Kospi rose 2.47 percent to 2,944.45 points on Monday. 

Over 4.9 million additional shares held by institutional investors, or 37 percent of the total, became eligible for trading Monday after six months of a lock-in period. 

As some investors cashed in after the mandatory lock-up, the trading volume increased to 3.3 million shares by close, compared with the average 173,000 shares of the last five trading sessions.

SK Biopharm made a hot debut on July 2 in one of the most successful IPOs in 2020. The stock price of the company soared 244 percent to 169,000 won on Dec. 30 from its IPO price of 49,000 won.

Eugene Investment and Securities on Monday downgraded its rating to hold from buy even though it raised the target price from 110,000 won to 150,000 won.

“The increase in the company’s stock price was bigger than expected, putting the company’s valuation higher than its competitors,” Han Hyung-hwa, an analyst with Eugene Investment and Securities, wrote in a research paper Monday.

Meanwhile, the company announced in a regulatory filing the same day that it agreed to sell a 12 percent stake it holds in Arvelle Therapeutics, a Switzerland-based biopharmaceutical company, to Angelini Pharma for 59.8 billion won.

By Park Ga-young (gypark@heraldcorp.com)