The Baggies played out an astonishing 5-5 draw with Manchester United on Sunday to take their points tally for the campaign to 49 and secure eighth place.
Foster is delighted with the progress West Brom have made and thinks they showed their fighting spirit in the ten-goal thriller with United.
"I am really happy to finish eighth," he said in the Daily Mirror. "It is the best season since 1981.
"We are proud and have been in the top eight all season. We have 49 points and that is an improvement on last season.
"I don't think anyone can complain."
The game against United marked Sir Alex Ferguson's final match before retirement and Foster believes it was a fitting farewell for the legendary manager.
He said: "We did start slow but United were incredible. We got a few murmurs as soon as it went to 5-2.
"But, when we knocked the third in, the atmosphere was amazing and everyone enjoyed it. Fair play to us for getting back into it.
"I enjoyed it, even conceding five. It was like a show with Alex retiring. It was brilliant to be a part of and a good way to send him off, even though they didn't win.
"United probably took their foot off the gas and allowed us to get back in. It was a joke of a game. It could have been 9-9."