The Baggies have reached the 40 point mark, a total which is accepted as meaning safety from relegation.
Foster said: "Nobody here is treating the rest of the season as a holiday just because we're nearly safe.
"I think people were starting to think (before the two wins) that we'd switched off and that we were going to coast to the end of the season.
"That hurt us to be truthful because that isn't the way that this team is. The bunch of lads we have are not like that."
Foster added: "We are as hungry to win games now as we were back in August. We go into games wanting desperately to win.
"We want to build on the great start we had and finish as high up in the table as we possibly can."