Blake Harrison (Neil) previously suggested that continuing the sitcom past three series would be "weird".
In an interview with BBC News, his co-stars James Buckley (Jay) and Simon Bird (Will) agreed that a fourth series would be "contrived".
"I don't think there ever will be another [series] after this one," said Buckley. "I think we'd all want to do another series. We'd milk it dry to be honest, but we don't want to do it badly."
"If [the writers] have an idea where those four characters would still be together after school's finished, then maybe [it could continue], but because the series ends with school finishing, it seems natural that they would all go their separate ways," said Bird.
He added: "It's so nice and rare to have a comedy show that is so popular. We don't want to ruin that."
The third series of The Inbetweeners begins tonight at 10pm on E4.