Production will start in the first half of 2017, the South Korean tech giant said.
The Pyeongtaek semiconductor plant will be built at a total cost of 15.6 trillion won, the largest investment by Samsung in a single production line.
Among those present at the ground-breaking ceremony were President Park Geun-hye; Lee Jay-yong, the company's vice chairman; and officials from the government and related companies.
Currently, Samsung has two chipmaking facilities in Giheung and Hwaseong, also located in Gyeonggi Province.
Samsung took up 40.4 percent of the global DRAM (dynamic random access memory) market in 2014, up from 36.2 percent held in the previous year, according to data compiled by U.S. market research firm IHS.
Its compatriot SK hynix had a 27.4 percent share, compared with a combined 24.6 percent for U.S. Micron Technology and Japan-based Elpida Memory. Micron acquired Elpida in 2013. In 2013, SK hynix took a 26.8 percent share, closely trailing Micron-Elpida with 28.3 percent.