Preheat oven to 350-degrees F. Prep a large baking sheet by lining with parchment, baking mat, or with butter and flour.
In a bowl whisk together flour, cocoa powder, baking soda, and salt.
In a separate bowl, using an electric mixer beat together butter and granulated sugar until light and fluffy. Add eggs and beat until combined well. Add vanilla extract and combine well.
Add flour mixture to butter mixture and mix to form a stiff dough. Fold in chocolate chips until combined.
Divide dough in half. Flour or slightly wet your hands and form dough into two slightly flattened logs on prepared baking sheets, each approximately 12 inches long and 2 inches wide.
Bake 30-35 minutes, or until slightly firm to the touch. Cool on baking sheet 5 minutes, or long enough to handle easily.
Transfer to cutting board and cut diagonally into 3/4 inch slices.
Arrange biscotti, cut sides down, on the baking sheet and bake for about 10 minutes, or until crisp.
Cool on a rack.