Preheat oven to 350°F. Grease a 9x13 inch baking pan.
In a medium bowl, combine melted butter, graham cracker crumbs and 1/4 cup sugar. Press into the bottom of the prepared pan.
In a large bowl, beat cream cheese until smooth. Beat in 1/2 cup sugar until blended. Add eggs one at a time, beating after each addition. Beat in vanilla extract.
Stir in flour and mix until just blended. Pour over the crust.
Bake for 25 minutes or until golden brown.
In a small saucepan over low heat, melt sweetened condensed milk and chocolate chips together until smooth. Pour over cheesecake layer and spread evenly.
Bake for an additional 20 minutes or until golden brown.
Allow to cool completely before cutting into bars.