Despite having the world's richest league, England go into the competition in France having not won a major tournament since landing the 1966 World Cup on home soil.
"England beat us 3-2 in Berlin (in March) but I do not know if in matters of quality and consistency they have enough for an entire tournament," Boateng told German Railway DB Mobil magazine.
Roy Hodgson's men came from two goals down to defeat the world champions in their friendly earlier this year.
"Spain, France and Belgium are in my opinion candidates for the semi-finals," said Boateng. "Along with our team of course."
The Germans, who won the World Cup for a fourth time in 2014, have reached at least the semi-finals of every major tournament since 2006 and face Ukraine, Poland and Northern Ireland in the Euro 2016 group stages.
England take on Russia, Slovakia and Wales in Group B of the 24-team tournament that starts on June 10.
(Reporting by Karolos Grohmann; Editing by Tony Jimenez)
