How do you write half million in words?

Answer 1

That is the correct spelling of "half million" (500,000). The terminology for the determiner (adjective) would properly be "a half million" or "one-half million" or more colloquially "half a million."

e.g.

There were a half million refugees from the flood.

More than one-half million residents were without power.

As many as half a million cars were affected by the recall.