Slightly over 8 percent of South Korea's major listed companies suffered a double whammy of operating and net losses in 2015 amid an economic slump, data showed Wednesday, sparking concern over their financial health.

According to the data by the Korea 20000 Corporate Research Institute, 23 of the 273 listed companies with sales of at least 500 billion won ($447 million), or 8.4 percent, reported both operating and net losses last year.

Of the total, 27 companies posted operating losses, while 55 firms registered net losses.

The data also showed 11 of the 23 companies having a debt-to-equity ratio in excess of 200 percent.

As of end-2015, troubled Daewoo Shipbuilding & Marine Engineering Co., which logged both operating and net losses, had a debt ratio of over 7,000 percent.

The debt ratio of STX Offshore & Shipbuilding Co., another struggling shipyard, stood at more than 1,300 percent after registering both operating and net losses.

Hyundai Merchant Marine Co., the country's No. 2 shipping line that was separated from Hyundai Group last month following a cash crunch, posted a debt ratio of 1,565 percent. The company chalked up a net loss of some 600 billion won last year.

Hanjin Shipping Co., South Korea's largest shipper, reported a debt ratio of 817 percent as of the end of last year, which worsened to 1,011 percent in the first half of this year.

Creditors on Tuesday decided not to extend additional support to the cash-strapped shipper, triggering speculation about its possible court receivership.

According to the data, 40 listed companies in South Korea had a debt-equity ratio exceeding 400 percent as of end-2015. Of them, 21 saw their financial soundness worsen over the past half year, with seven suffering impaired capital. (Yonhap)