Line a 9" x 13" baking pan with aluminum foil or parchment paper, leaving an overhang for easy removal; set aside.
In a large bowl, stir together 3 and ½ cups old-fashioned oats, 2 cups crispy rice cereal, and ¾ cup raisins.
In a medium saucepan combine ½ cup unsalted butter, ½ cup honey, and ⅔ cup light brown sugar.
Place the saucepan over medium heat and bring the mixture to a boil, stirring occasionally.
Reduce the heat to low and simmer for 3 to 4 minutes, stirring often, until the sugar dissolves.
Remove the pan from the heat and stir in 1 teaspoon vanilla extract.
Pour the hot butter-honey-sugar mixture over the oat mixture and stir with a wooden spoon or spatula until the cereal and raisins are evenly coated.
Scrape the coated cereal mixture into the prepared pan and spread into an even layer.
Immediately sprinkle ½ cup semi-sweet chocolate (small chunks or mini chips) evenly over the top.
Press the chocolate and cereal mixture firmly and evenly into the pan with a metal spatula to compact the bars.
Let the bars set at room temperature for at least 2 hours, until firm.
Use the foil or parchment overhang to lift the set slab from the pan and cut into 12 to 14 bars. Wrap bars in parchment paper and store in an airtight container for up to 2 weeks.