How can I simulate the breakdown voltage of a device? I'm trying to characterize a grounded gate MOSFETs using a DC sweep but I don't see anything happening

@Leonardo Gomes Unfortunately, this is often not modelled. Also the dc behaviour of ESD elements is mostly only modelled for parasitic effects like capacitance and leakage current, but not for realistic behaviour during an ESD event.

Snap... I'm worried about the protection level of the GG MOSFET and/or pwell diodes, for both antenna effects and ESD. The diodes are rated for 5.5V, and I'm not sure if they will protect the thin oxide gates in any way.

For breakdown voltage, I saw one way to model your transistor with a network of several transistors. But you might want to look beyond SPICE and try TCAD device simulation software instead.