Abstract: A method is provided for making certain diaryliodonium salt photoinitiators, based on the initial formation of diaryliodonium perchlorate which is formed from a diaryliodonium bisulfate precursor. The diaryliodonium perchlorate is then reacted with a counter ion source, such as an alkali metal hexafluoro metalloid salt, to produce the desired diaryliodonium salt, which can be used as a photoinitiator. The iodonium salt photoinitiators made by the method of the present invention can be used to effect the cure of a variety of cationically polymerizable organic materials, such as epoxy resins.