Preheat oven to 350 degrees F (175 degrees C). Grease cookie sheets.
In a large bowl, cream together the butter, white sugar and brown sugar until smooth.
Beat in the eggs one at a time, then stir in the vanilla. Dissolve baking soda in hot water. Add to batter along with the peanut butter. Stir in the flour.
Drop by teaspoonfuls onto ungreased cookie sheets.
Bake for 8 to 10 minutes or until golden brown. Allow cookies to cool on baking sheet for 5 minutes before transferring to a wire rack to cool completely.