The five were convicted of attacking a freight ship in the Gulf of Aden in January 2009.
Prosecutors asked for a seven-year sentence, but the judge said he took into account the difficult conditions in Somalia that led the men to piracy.
"It is a lucky coincidence that nobody was killed or wounded" in the attack, said judge Klein Wolterink.
Other Somali piracy suspects are being held in France, Spain, Germany and the U.S.
Kenya has convicted 18 pirates since 2007. More than 100 await trial there.
