Most of the huge banks we list earlier are providing high interest on the money you will deposit on fixed savings plans. You leave your money and every month, you can enjoy great ROI on your investments in USD. Here some examples for a one year fixed plan :
Acleda Bank 4.25% (paid monthly) annually or 4.50% (paid at maturity)
ABA Bank 3.25% (paid monthly) annually or 3.50% (paid at maturity)
LOLC 7.75% (paid monthly) annually or 8.00%  (paid at maturity)
If you become cambodian resident (you live there more than 6 months), you won’t have any tax on those interests that can provide you significant income and growth of your savings every year. Some fixed plans for 24 months and even for 3 years provide up to 8.5% of yearly interest.