In a large bowl, cream together the butter and sugar until smooth.
Beat in the eggs, vanilla extract, and peppermint extract.
Combine the flour, cocoa powder, baking soda, and salt; gradually stir into the creamed mixture.
Mix in the chocolate chips.
Drop by rounded spoonfuls onto ungreased cookie sheets.
Bake for 8 to 10 minutes in the preheated oven, or until set. Allow cookies to cool on baking sheet for 5 minutes before removing to a wire rack to cool completely.