In a small saucepan, combine the sugar and 1/2 cup water over medium heat. Bring to a boil, then reduce the heat and simmer, stirring occasionally, until the sugar has dissolved, about 5 minutes. Remove the pan from the heat and allow the syrup to cool, about 15 minutes.
In a blender, puree the syrup, vodka, vermouth, lime juice and pears until smooth. For each drink, pour some of the pear mixture into an ice-filled cocktail shaker and shake well. Pour into a chilled martini glass. Garnish with pear slices and serve.