Semmy started his fight career in the MMA with Pancrase: a fight discipline in which the fighters use punches with open hand, kicks, throws, ground fighting with arm, leg, and heel clamps, and strangulations. The practices and games at the Pancrase always come with sportsmanship and respect towards the opponent.

Sem has won three times the title "King of Pancrase". After his victories over Manabu Yamada, Guy Mezger, Takaku Fuke and Osami Shibuya, Sem left the Pancrase and went for the big time in America, namely in the UFC (Ultimate Fighting Championship) and PRIDE (Japan). He fought against Pete Williams, Josh Barnett, Fedor Emelianenko, Gan McGee, Gilbert Yvel and many others. Another well known Pancrase fighter is Bas Rutten.

The difference between UFC and Pancrase is in the technique of striking: in the UFC a fighter punches with his fist and in Pancrase with his open hand.
In America there are currently two unions that represent the MMA: the UFC fighters and strike Force. It is allmost impossible for fighters of the different federations to fight eachother. Until the end of 2006 the UFC and PRIDE were the largest unions until the UFC acquired all rights of PRIDE and became the largest MMA organization in the world.