Alexander Onischuk (Ukrainian: ????????? ?????????? ??????, romanized: Oleksandr Vasyl'ovych Onishchuk; born September 3, 1975) is a Ukrainian-American chess grandmaster.
He competed in the FIDE World Chess Championship in 2000 and 2004, and in the FIDE World Cup in 2005, 2007, 2009, 2011, 2013, 2015 and 2017.