A professional competitor since 1999, he was a cast member of Spike TV's The Ultimate Fighter 5, and also competed in World Extreme Cagefighting (WEC) and King of the Cage (KOTC).
Shortly after his arrival, he began training in judo at Gokor Chivichyan and Gene LeBell's Hayastan MMA Academy, quickly becoming one of the top judokan in the country, winning junior nationals less than two years later.
He won his first four fights, then lost a decision to future UFC Lightweight Champion Sean Sherk in 2001.
[4] In 2007, Gamburyan appeared on the reality show The Ultimate Fighter 5, fighting on Jens Pulver's team.
[6] In the semifinal round, Gamburyan beat Joe Lauzon in a unanimous decision and advanced to the finale with Nate Diaz.
After the Lauzon fight, UFC president Dana White personally apologized to Gamburyan for doubting him.
[7] In the finale, Gamburyan controlled Diaz for the majority of the fight, but was forced to tap out in the second round after dislocating his right shoulder on an unsuccessful takedown attempt.
[8] Although this technically counts as a submission due to injury, Gamburyan has never been submitted by an opponent in his MMA career.
[10] Gamburyan raised some controversy in the Cox fight by delivering a spinning leg kick after feigning the mutual tap of gloves that is often seen at the beginning of the match.
[22] Gamburyan was expected to face Raphael Assunção on March 19, 2011, at UFC 128,[23] but was forced out of the bout with a back injury[24] and replaced by Erik Koch.
Gamburyan was expected to face Diego Nunes on September 24, 2011, at UFC 135,[27] but was forced to withdraw from the bout after suffering a shoulder injury.
Subsequently, Siver failed a post fight drug screening, testing positive for banned substances.
[48] However, Gamburyan pulled out of the fight in mid-August for undisclosed personal reasons and was replaced by Albert Morales.