Multiple screens show stocks traded at Nextrade, the country's first alternative stock exchange, at Nextrade's headquarters in Seoul's financial district of Yeouido, March 17. Yonhap

Park Suk-jun, an office worker at an electronics company, says he is no longer tempted to trade stocks during work hours after Nextrade, the country's first alternative stock exchange, launched on March 4.

Nextrade operates from 8 a.m. to 8 p.m. on weekdays, longer than the trading hours of the Korea Exchange (KRX), the country's main securities exchange operator, which runs from 9 a.m. to 3:30 p.m.

"Thanks to Nextrade, I can sell and buy stocks even after I get off work at 6 p.m. and both the KOSPI and Kosdaq are closed," Park said, referring to the two stock exchanges run by KRX.

Park is among more than 14 million retail investors nationwide who have become the most active users of Nextrade.

According to Nextrade, retail investors accounted for 98 percent of the transaction volume, which totaled 136.91 billion won ($93.1 million) in the first two weeks after its opening.

"Many of these investors are daytime salaried workers who work in industries other than the securities sector, and therefore can't freely trade stocks during working hours," Jung Eui-jung, head of the Korean Stockholders' Alliance, said. "Under the circumstances, the dominant proportion of retail investors as Nextrade users shows the trading platform perfectly satisfies their demand for longer trading hours."

Industry officials said retail investors could boost the popularity of Nextrade as a new trading platform, noting that it accounted for more than 30 percent of the country's total stock transaction volume during the first five trading days after its opening.

This proportion was higher than expected, considering Nextrade had planned to increase its market share by a modest 10 percent over the next three years.

The trading of more large-cap stocks will help Nextrade gain ground, they said, pointing out that a total of 145 trending stocks from KOSPI and 95 from Kosdaq are available for trading starting Monday.

The KOSPI includes bellwether Samsung Electronics, its cross-town rival SK hynix, as well as Meritz Financial Group and Kakao.

The Kosdaq includes K-pop powerhouse JYP Entertainment, battery materials manufacturer EcoPro BM, and pioneering pharmaceuticals company HLB.

The inclusion of the aforementioned 240 stocks comes after Nextrade started with just 10 stocks, and the number is set to expand to 800 by mid-April.

In a bid to attract more retail investors, Nextrade plans to waive trading fees for all transactions from April 4 to 30.

"For small investors, the fees matter a lot concerning their profits and that Nextrade is right on track in its strategy," Jung said.