Chipguy,
" Your individual FET must be quite brilliant to
discern the operating frequency's specific contribution to its"
Now you're just being arguementative. It's a pretty simple concept. Of couse the package and heatsink are not varying. Increasing the frequency increses the power dissipation which increases the temperature, which increases the leakage. At a high enough (local, on-chip) temperature, thermal energy will be enough to generate electron-hole pairs that are available for conduction across the channel. This carrier generation should increase exponentially as the thermal energy approaches that of the bandgap energy, and result in an avalanche process.
Pravin.