What is the Effect of Floating MOSFET Base Plate?

[EE4me]

TL;DR

Are there any downsides to leaving a MOSFET base plate floating?

My specific system will benefit from having the MOSFET base plate floating. Are there any downsides to leaving a MOSFET base plate floating? Are there any reasons not to?

 

[Baluncore]

Are there any downsides to leaving a MOSFET base plate floating?

Base plate ? = body ? substrate ?
It is usual to connect the substrate to the source terminal so as to prevent voltage breakdown, ESD, and to maintain isolation by reverse biasing the PN contact layer on the substrate.
What voltage will it acquire if it is left to float ?
https://en.wikipedia.org/wiki/MOSFET#Body_effect

 

[DaveE]

This depends on the specific device and the circuit/application. Usually the "base plate" is connected to the drain, so it won't be truly floating. You won't get a useful answer from us without providing more information. You could start with a schematic, the part number of the MOSFET, and a description of what you want your circuit to do.