In a large heavy saucepan, combine the sugar, butter and water; bring to a boil, stirring constantly. Remove from the heat; stir in 2 cups chocolate chips until melted. Cool slightly.
In a large bowl, beat eggs and vanilla; stir in chocolate mixture. In another bowl, mix the flour, baking soda and salt; gradually add to chocolate mixture, mixing well. Stir in remaining chocolate chips.
Spread into a greased 13-in. x 9-in. baking pan. Bake at 325° for 35-40 minutes or until a toothpick inserted in center comes out clean. Cool completely in pan on a wire rack.
Sprinkle with confectioners' sugar. Cut into bars. Store in an airtight container.