Arrange oven rack to middle of oven. Preheat oven to 350 degrees.
Line a baking sheet with parchment paper.
In a bowl, whisk together flour, cocoa, baking soda and salt.
Beat the butter using a kitchen aid mixemixer on medium until fluffy.
Add the sugar to butter and mix on high until well combined. Add eggs, one at a time, and then vanilla. Continue miximixing until combined.
Turn mixer speed down to low and then carefully add flour a little at a time.
Mix dough until it comes together and flour is well combined.
Stir in chocolate chips.
Divide dough iin half. Take each half and form a flat loaf that is about 12" long and 2" - 3" wide on the parchment paper. Each loloaf should be about 4" apart.
Bake for 30- 40 minutes or until the loaf is firm with a few cracks on top.
Remove and slide parchment onto a cooling rack. cool for 10 minutes. Be sure not to cool for more time or the loaf will fall apart when you try to cut it.
Lower oven temperature to 300 degrees.
After 10 minutes, cut each loaf at a slight diagonal into 12 slices.
Arrange the cut slices on the baking sheet standing up on flat side.
Bake for 10 minutes or until the sides feel dry and have crumbs.
Cool the biscotti on a cooling rack. While cooling, sprinkle with powdered sugar.