Four Korean companies -- Hanwha Aerospace, Cosmo Advanced Materials, KT and Posco International -- were included to the Korean index powered by US index provider Morgan Stanley Capital International on Friday.

The much-anticipated inclusion of battery material firm EcoPro fell through due to its recent "extreme" price surge.

Hanwha Aerospace, the space business arm of South Korean conglomerate Hanwha; battery material firm Cosmo Advanced Materials; telecommunications firm KT; and Posco International, Posco Group's general trading arm were added to the Korean Index under the quarterly readjustment announced Friday. Meanwhile, advertising agency Cheil Worldwide, Lotte Shopping, security firm S-1 Corp and COVID-19 test kit developer SD Biosensor were dropped from the list.

The change is set to take effect after the market closes on May 31.

The inclusion opens new opportunities for the firms as passive funds, which track market indices, are likely to buy the newly added stocks.

EcoPro's failure to make it to the index appears to have been caused by its sharp surge in stock price in a short-term period.

EcoPro's share price rose from 110,000 won ($82.50) to 550,000 won between Jan. 2 and Thursday, experiencing a fivefold increase due to retail investors’ expectations for the Korean battery industry to boom.

“EcoPro seems to have not made the list due to the recent extreme price surge, as the evaluation was made on April 18,” Shinhan Securities analyst Lee Jae-rim said.

The shares of EcoPro peaked in mid-April, hitting its highest closing price of 769,000 won on April 11.

“It is the first incident of a share not making the list in Korea for such a reason,” Lee said, adding that the battery material firm could make the list in the next set of readjustments slated to take place in August.

Meanwhile, the decision for South Korea's potential upgrade to a developed market classification by the MSCI will come out in June, when the index provider releases its annual publication.

Listed on the Emerging Markets Index by the MSCI, Korea has been seeking a promotion to the Developed Market Index -- the top grade of stock indices -- for more than a decade in hopes to attract more global investors and prove the credibility of the local financial market.

The government and financial authorities have been introducing new measures to improve the financial market, such as extending the hours of operation of the foreign exchange market, mandating English-language disclosures from listed firms and more.