Tim is right, it is an identical chip until Intel gets their greedy little hands on it and cuts the multiplier on it by 1x.
There are a number of reasons or possibilities why Intel does this but as each chip is tested, some pass all the tests with a 23x multiplier setting and thus become the i3 540. Others fail with the 23x multiplier setting but pass with the 22x multiplier setting and thus become the 530.....