This article reviews how assumptions about MOSFET switching behavior are used to calculate switching loss accurately in planar MOSFETs. It then explains why these assumptions are not valid in superjunction and other RESURF MOSFETs, leading to overestimations when the switching loss equation is applied. Essentially, the period of voltage-current overlap in RESURF devices differs from that of planar transistors due to evolutions in capacitance characteristics.