Bring sugar and water to a boil (this happens quickly!) with rosemary stirred into it.
Stirring often, boil for 1 minute or until sugar is dissolved.
Remove from heat, place into fridge and let sit for 30 minutes.
If possible, run the liquid through a sieve or cheesecloth.
Chill for 4 hours.
Notes
Sometimes I don't chill it because it's going into my Rosemary Grapefruit Mimosa's right away. Just be sure to get it cooled down so it doesn't warm your drink... gross!