South Korea's top 10 listed firms by market capitalization saw their presence on the main bourse decline this year, due mainly to falling share prices of market bellwether Samsung Electronics Co. and other market heavyweights, data showed Thursday. The combined market cap of the top 10 firms came to 433.79 trillion won (US$407 billion) as of Wednesday, accounting for 33.94 percent of the total, according to the data by the bourse operator Korea Exchange (KRX).