In an electric mixer, cream together the butter and sugar until light in color. Add the eggs, vanilla and salt and cream until fluffy. Add the cocoa powder, baking soda and flour all at once and mix until thoroughly incorporated, but do not over mix. Stir in the chocolate chips and mix until just incorporated. Drop spoonfuls of dough onto lightly oiled baking sheets and bake approximately 10 minutes, or until just set. Remove the pans from the oven and allow to cool for 2 minutes. Carefully remove the cookies to a wire rack and allow to cool completely.