Why would I need to?
A semiconductor turns on at a specified voltage threshold, they aren't averaging the Vpp to turn it into RMS, they are reacting to the actual potential difference between two points, and a Vpp is the Min and Max of the voltage, the difference between those levels is the voltage that a semiconductor will react to.
In some cases it could be the peak voltage rather than peak to peak, it really depends on the circuit in use, either way it isn't RMS.