Move oven rack to lowest position. Heat oven to 375?. Mix cake as directed on package. Measure 4 cups batter into separate bowl; sift cocoa gradually over this batter, folding until well blended, being careful not to deflate batter. Alternately spoon plain and chocolate batters into ungreased 10-inch tube pan.

Bake 30 to 35 minutes or until top crust is firm and looks very dry. Do not under bake. Invert pan on heat-proof funnel or bottle; cool completely, at least 1 1/2 hours.

Carefully run knife alongside of pan to loosen cake; remove from pan. Place on serving plate; drizzle with chocolate glaze.

Chocolate glaze: in a small saucepan, combine sugar and water. Cook over medium heat, stirring constantly, until mixture boils. Stir until sugar dissolves; remove from heat. Immediately add chocolate chips; stir until chips are melted and mixture is smooth. Cool to desired consistency; use immediately.