In large bowl, combine raspberries and peach slices. Sprinkle 1/2 cup ofthe sugar over fruit; let stand 1 to 2 hours.
Drain liquid from fruit; add water to measure 1 cup. In medium saucepan, combine remaining 1/4 cup sugar and cornstarch; mix well. Add fruit liquid; blend well. Cook over medium heat for 5 minutes or until thickened and clear, stirring constantly.
Remove from heat; gently stir in fruit. Serve warm or cool.