Heat oven to 350°F (325°F for dark or nonstick pan). In medium bowl, cut 6 tablespoons butter into cake mix, using pastry blender (or pulling 2 table knives through ingredients in opposite directions), until crumbly. Press firmly in bottom of ungreased 13x9-inch pan. Bake 13 to 14 minutes or until crust is dry.
Sprinkle pecan halves evenly over baked layer. In 2-quart saucepan, heat 2/3 cup butter and the brown sugar to boiling over medium heat, stirring occasionally; boil and stir 1 minute. Spoon mixture evenly over pecans.
Bake 13 to 16 minutes or until bubbly and light brown. Sprinkle chocolate chips over warm bars. Cool completely, about 1 hour. For bars, cut into 8 rows by 4 rows. Store covered.