Heat oven to 350°F.
Grease 13x9x2-inch baking pan or two 8-inch square baking pans.
Stir together cocoa and baking soda in large bowl; stir in 1/3 cup butter.
Add boiling water; stir until mixture thickens.
Stir in sugar, eggs and remaining ⅓ cup butter; stir until smooth.
Add flour, vanilla and salt; blend completely.
Stir in chocolate chips.
Pour into prepared pan.
Bake 35 to 40 minutes for rectangular pan, 30 to 35 minutes for square pans or until brownies begin to pull away from sides of pan.
Cool completely in pan on wire rack.
Cut into squares.
