Preheat the oven to 300 degrees F (150 degrees C). In a small bowl, whisk together the flour, baking soda, salt and cocoa. Set aside.
In a large bowl, cream together the butter, brown sugar and white sugar until smooth. Beat in the eggs, one at a time, then stir in the vanilla. Gradually blend in the dry ingredients until just moistened, then stir in the peanut butter chips. Drop by rounded spoonfuls onto the prepared cookie sheet.