The Dutch surprisingly lost 1-0 to Denmark in their Group B opener and will be unable to reach the knockout stage if they lose to Germany later on Wednesday in Kharkiv, and Denmark take a point against Portugal in the earlier game in Lviv.
"Our goal is, as ever, to reach the semi-final but that goal was named in 2005," Van Oostveen said in an interview with Dutch newspaper Metro.
"That is our ambition and fits our fourth place on the FIFA rankings and the fact that we are almost always present during finals.
"If we go out earlier there are no consequences. Both sides signed a deal with a healthy mind."
Van Marwijk succeeded Marco van Basten in 2008 after the Dutch were eliminated in the quarter-finals of that year's European Championship by Russia.
At the 2010 World Cup he guided the national team to their third World Cup final before losing to Spain.
Last year Van Marwijk extended his original four-year deal until 2016.
"The extension is based on our long-term policy," added Van Oostveen.
"We want our team to play recognisable football with our own identity and style.
"And if you see our results under Van Marwijk our opponents are still looking for the solution to beat us. But you can always lose a match."
