A US court heard that John William Racine II, from Los Angeles, rerouted visitors to a page featuring an American flag and the motto "Let Freedom Ring".
At a sentencing hearing on Wednesday, US District Judge Howard Matz told the web designer: "I don't think of you as an evil person... but this was a crime. It wasn't just a childish prank."
Matz sentenced Racine, 24, to 1000 hours of community service and a $2000 fine.
Racine, also known as John Buffo, vowed to the judge he would never do such a thing again.
"I don't think of you as an evil person... but this was a crime. It wasn't just a childish prank"
Judge Howard Metz to John William Racine II
Prosecutors said Aljazeera did not respond to US government inquiries about whether the hacking caused it any financial losses.
Racine posed as an Aljazeera employee to get a password to the network's site, then redirected visitors to the new page he created.
In June, Racine pleaded guilty to wire fraud and unlawful interception of an electronic communication.
Many Americans were upset at Aljazeera's reporting of the Iraq war, and accused the broadcaster of anti-US bias.
However, Aljazeera said it was committed to presenting both sides of the story impartially.