Here's why:
* Oxymoron: An oxymoron combines two contradictory terms to create a surprising effect. Examples: deafening silence, living dead.
* Half-asleep: This phrase describes a state of being partially awake and partially asleep. It's not contradictory, as both "half" and "asleep" can exist simultaneously.
Therefore, "half-asleep" is simply a descriptive phrase, not an oxymoron.