Gestern habe ich eine halbe Stunde im Park gelesen.
Yesterday I read in the park for half an hour.
Das Essen wird in einer halben Stunde fertig sein.
The food will be ready in half an hour.
Note
The article is part of the word: die halbe Stunde. That way you learn the gender with it.
Remember die halbe Stunde for good. ripiti brings the word back just before you forget it, with these sentences. Free, no account needed, works offline.