Italy meet Northern Ireland and if they win, they will face either Wales or Bosnia-Herzegovina for a place in the World Cup this summer.
"We shouldn't have any doubt, our focus is only on Northern Ireland and the semi-final," Buffon told BBC Sport.
"Then, if we're happy, we'll think about the final against Wales or Bosnia.
"But for the last four months, our only focus has been on Northern Ireland, because that's the way it is.
"Northern Ireland are the first obstacle, and they are a team that deserves our respect."
Italy meet Northern Ireland in Bergamo on Thursday night, where the Azzurri are unbeaten under coach Rino Gattuso.
Juventus great Buffon added: "When the coach played his first game (against Estonia) we had a great win, and that evening we remember it was a great atmosphere and there was great support.
"The first half ended 0–0, but the people understood the effort that the team was giving and they supported us.
"This is something, a detail, that is in the minds of the staff and in the minds of the players, so it is very important."