Preheat the oven to 250 degrees F (95 degrees C). Place popped popcorn in a very large bowl.
Melt the butter in a large saucepan over medium heat. Then stir in the brown sugar, corn syrup and salt. Bring this mixture to a boil, stirring constantly. Then boil without stirring for approximately 4 minutes. Remove from the heat and then stir in the baking soda and vanilla extract.
Pour the caramel sauce over the popcorn and stir it to coat all the popcorn with the caramel sauce.
Place the popcorn in a roasting pan, two large shallow baking dishes or pans and bake in a preheated oven, for approximately 30 minutes (stirring halfway through).
Chop up the snickers bars. Stir the snicker pieces into the caramel popcorn and cook for 5 more minutes for the snicker pieces to soften.
Then remove the popcorn from the oven and place on a baking sheet to cool. While the popcorn is cooling, melt the semi-sweet chocolate chips.
Place the chocolate in a microwave safe bowl. Heat in 30 second intervals, stirring after each interval until melted. Use a fork to drizzle the chocolate over the popcorn. Let the popcorn sit for 10-15 minutes for the chocolate to set.
Then the popcorn is ready to break apart into pieces and enjoy!