Add all ingredients to a small pot. Simmer until sugar is completely dissolved for about 5-10 minutes. Remove from heat. Cool and strain. Refrigerate until ready to use.
Cocktail
Fill 2 lowball glasses with ice. Divide vodka between the two glasses. Add 2 tablespoons of simple syrup and 1/3 cup pear juice to each. Garnish with pear slices and rosemary.