The announcement follows repeated calls from new South Korean President Moon Jae-in for big businesses to invest more domestically as part of a wider job-creation agenda.
The world's top maker of smartphones and memory chips said it would spend 14.4 trillion won on expanding its new NAND factory in Pyeongtaek by 2021, and 6 trillion won on upgrading a new semiconductor production line in Hwaseong.
Samsung said its plan could open up to 440,000 roles by 2021.
Analysts say Samsung's investment seeks to widen the gap in technologies.
The investment may ease shareholders' concerns over a series of delayed big decisions due to the absence of the head of Samsung Group Jay Y. Lee.
"Samsung is being more aggressive in domestic investments because of the current (political) climate", said Park Ju-gun, head of corporate analysis firm CEO Score. Global tech companies have been increasing servers and data centers to handle more data from mobile devices and auto vehicles and also on expectations that adoption of artificial intelligence would create even more demand for handling data.
Mass production of the latest V-NAND chips at the new plant is part of Samsung's strategy to focus its capacities on the growing NAND chip market that is estimated to expand almost 40 percent every year.
Some analysts said the additional capacity could cause slight oversupply in early 2018, but that price crashes are unlikely as smartphone makers opt for greater internal storage.
It did not elaborate on when and how much money it plans to invest there.
The facility will focus on the production of Samsung's fourth-generation 64-layer V-NAND chips, adding to the company's capacity for cutting-edge memory products, the firm said.
In China, some South Korean firms have suffered from sales decline or have been forced to scale down operations after retaliatory measures from Beijing over the deployment of a United States anti-missile defence system outside Seoul, but component makers such as Samsung have not yet been affected.
Samsung Display Co., meanwhile, is also considering establishing a new production line for organic light-emitting diode (OLED) products in Asan of South Chungcheong Province.
In smartphones, Samsung has been increasingly sandwiched by smaller Chinese rivals in the low and mid-end markets, and by Apple's iPhone in the high-end segment.