The Apple A4, which by all accounts is still commercially viable given the price of used Apple products on craigslist, measured in at 53.3 mm². Only two (and a half?) generations later, we have the Apple A5X weighing in at 165 mm² – a whopping 310% larger. Remember that all three of the Apple processors we are comparing here are (basically) at the same 45 nm generation, so we have a genuine apples-to-apples comparison (sorry about the bad pun). By way of further comparison, another flagship applications processor, the NVIDIA Tegra 3 is 82 mm², and fabricated in a similar 40 nm generation by TSMC, so it is (more or less) consistent with the prior generation A5.
If anyone wonders why the New iPad gets hotter than the previous one, this is a big reason why. The A5X is a huge chip for a mobile device. I don’t expect the next iPhone to have that kind of chip, unless Apple is going to move to a bigger phone.