Samuel Untermyer II, (1912 - 2001) was a United States nuclear engineer who theorised that steam bubble formation in a nuclear reactor core would not produce unstable reactions but would instead result in an inherently stable and self-controlling reactor design. He was responsible for the BORAX Experiments and in recognition of his fundamental development work on safe, water-cooled reactors the American Nuclear Society now has an award named after him for work in this field.
He was the grandson of Samuel Untermyer.
He was awarded the Newcomen Medal in 1980.