Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13 inch baking pan.
In a large bowl, cream together the butter, white sugar and brown sugar. Beat in the eggs, one at a time, then stir in the 3/4 cup peanut butter. Combine the oats, flour and baking soda; stir into the creamed mixture until well blended. Press the dough evenly into the prepared pan.
Bake for 15 to 20 minutes in the preheated oven, until firm. In the microwave or over a double boiler, melt chocolate chips and 1/2 cup peanut butter together, stirring frequently until smooth. Spread over cooled bars and allow to set up before cutting into squares.