How was Kary B. Mullis awarded the Nobel Prize?

Name: Kary B. Mullis. 
Country: United States.
Date of Birth: 28 December 1944.
Died: 7 August 2019.
The subject of Study: DNA polymerase chain reaction.
Noble Prize Year: Nobel Prize for Chemistry in 1993 for their invention of the polymerase chain reaction (PCR) technique.