Slice the bananas thinly (about 1/4" thick or less) and as uniformly as you can. Put them on a wire rack and the rack on a baking sheet. Put that in the oven on the lowest heat setting available and prop the door open an inch with a wooden spoon.
Check on them in about 4 hours - may take up to 12. They are done when they no longer feel sticky to the touch. If you don’t have a wire rack and place them directly on the baking sheet, make sure to turn them every couple of hours.
They will not have the same texture as store bought chips --more chewy – but they’re good. they may also get a little brown from oxidation. I’ve tried dipping them in an anti-browning solution (Vitamin C dissolved in water) but it doesn’t make much difference in the final result - and it’s only aesthetic anyway.