Fadil Rudolf S., 26, who received the longest prison term, had first travelled to Syria to join the Sunni militia group Junud al-Sham and in 2013 joined fighters of the Isis terror group.
"After his first return to Germany, he once again made himself available as a fighter for Isis over several weeks in July 2014," the court in the western city of Düsseldorf said in a statement.
"Later in January and in the summer of 2015, he also sought twice to travel to Syria to join Isis."
The other men, 24-year-old Mohamed A. and 26-year-old Mustafa P., were sentenced to two years and nine months for involvement in Junud al-Sham for several months in 2013.
"The confessions of the accused had a mitigating effect on their sentences," the court statement said.
Taking away citizenship
According to a report in the Funke Mediengruppe, Interior Minister Thomas de Maizière has drafted a law which would take German citizenship away from people with two passports who fight for terror groups abroad.
The draft law was criticized by Eva Högl, deputy leader of the Social Democrats (SPD) in the Bundestag (German parliament).
“This draft law is a contravention against the current principle that people keep their citizenship. Criminals must be punished in Germany,” she said.
Almost a third of those who have travelled abroad have returned and 140 were killed while abroad, while around 420 are still in Syria or Iraq.
Germany has so far been spared large-scale jihadist attacks.
But it was shaken by two assaults claimed by Isis and carried out by asylum seekers - an axe rampage on a train in Würzburg that injured five, and a suicide bombing in Ansbach in which 15 people were hurt.
Police said last month they had foiled an alleged plot by a Syrian refugee to bomb one of Berlin's airports.