In a large saucepan over medium heat, combine the sugar, corn syrup, water, and salt. Heat, stirring, to boiling, then continue to cook using a candy thermometer to monitor the temperature.
Beat the egg whites until they are stiff and form peaks. Don't use a plastic bowl for this. When the sugar solution comes to 270 degrees F, or the soft-crack stage, remove from the heat and pour the mixture in thin streams into the egg whites, blending completely with a mixer set on low speed. Continue to mix until the candy begins to harden to the consistency of dough. This may take as long as 20 minutes. At this point add the semi-sweet chocolate chips. Remember that the candy must already be at the consistency of dough when you add the chocolate; the nougat will thicken no more after the chocolate is added.
When the chocolate is thoroughly blended and the nougat has thickened, press it into a greased 9x9-inch pan. Refrigerate until firm, about 30 minutes.
With a sharp knife, cut the candy in half down the middle of the pan. Then cut across into 7 segments to create a total of 14 bars. Melt the milk chocolate chips in the microwave for 2 minutes on half power, stirring halfway through the heating time. Melt completely, but be careful not to overheat. Resting a bar on a fork dip each bar into the chocolate to coat completely and place on wax paper. Cool until firm at room temperature, 1 to 2 hours.