Combine sugar with water in a saucepan over medium-high heat, stirring until the sugar has dissolved and the mixture comes to a boil. Reduce heat to low and simmer for 5 minutes; remove from heat and let stand 5 more minutes.
Stir pear liqueur into the syrup and refrigerate for 1 hour.
Gently combine strawberries, blueberries, and blackberries in a large bowl and pour syrup over the berries to coat. Allow berries to stand for about 3 hours to absorb flavors. Mixture can stand up to 3 days if desired.
