I guess, you are referring to ESD strength in terms of tolerable voltage levels for standarized tests?
I doubt if it's reasonable to generalize the answer, but BJT junctions are basically able to adsorb a certain energy amount by avalanche breakdown. RF transistors with very small structures may be damaged by rather small ESD energy amounts however. It's not correct to say, BJT are unaffected by ESD.
Some MOSFET devices have zener protection circuits, so there ESD strength may be even higher than BJT. Unprotected MOSFET can be damaged however if moderate overvoltages are causing a gate oxyde breakdown.