Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a mixing bowl, combine flour, sugar, cocoa powder, baking soda, and salt.
In another bowl, beat eggs and vanilla extract. Gradually add to the dry ingredients, mixing until combined. Stir in chocolate chips.
Divide dough in half. Shape each half into a log about 12 inches long and 2 inches wide. Place on the prepared baking sheet.
Bake for 25 minutes or until firm. Remove from oven and let cool for 10 minutes.
Reduce oven temperature to 325°F (165°C). Cut logs diagonally into ¾-inch slices. Place slices cut side down on the baking sheet.
Bake for an additional 10 minutes, turn slices over, and bake for another 10 minutes or until crisp. Cool completely on a wire rack.