Combine water and sugar in a 1:1 ratio, and heat it until it just barely boils.
Add the rosemary and simmer until all the sugar disolves. let it sit for 20 minutes (ish). Stir it until the last of the sugar disolves.
Store it in the fridge.
I use one Cup of water and one Cup of sugar in a glass measuring cup, then microwave on high for two minutes. Then stir until the sugar is fully disoleved.
That's it.