An investigation, which lasted month and a half, was started after US DRAM maker Micron Technology filed a complaint with the international trade watchdog last month.
The decision could lead to the imposition of import duties on South Korean DRAM chips. The Department of Commerce will make that decision as part of its investigation, a preliminary determination of which is due on or about 27 January.
DRAMs are a common type of memory chip and can be found in almost every computer.
Billions of dollars of alleged subsidies were allegedly provided to South Korean DRAM makers including the two largest, Hynix Semiconductor and Samsung. Of those, some of the largest were allegedly extended to Hynix as the company teetered on the brink of bankruptcy several times as a result of low DRAM prices that hit the entire industry.
Earlier this year, the board of Hynix rejected a $3.1bn take-over bid by Micron after the price of the US company's stock, which made up part of the deal, fell and shaved $331m off the value of the shares on offer.
The European Union is carrying out a similar investigation after German chip maker Infineon Technologies filed a complaint.