In a medium bowl, stir together graham cracker crumbs, confectioners' sugar, peanut butter and melted butter. Press firmly into the bottom of a 9x13 inch pan. Melt chocolate chips over a double boiler or in the microwave, stirring occasionally. Spread melted chocolate over the crumb crust. Chill for about 5 minutes, then cut into bars before the chocolate is completely set, then chill until ready to serve.