Preheat oven to 250 degrees F (121 C) and position oven rack in the center of the oven.
Rinse and dry your sweet potatoes thoroughly and slice them as uniformly thin as possible (~1/8-1/16 inch thick slices). If you have a mandolin, use it. Otherwise, use a very sharp knife to get these uniformly thin. Know that chips that are too thick in parts won't crisp up all the way. Still delicious, just not "chip" crispiness.
Toss slices in a touch of olive oil to lightly coat, then sprinkle with salt. Lay out in a single layer on a parchment-lined baking sheet and bake for about 1 hour 30 minutes to 1 hour 45 minutes, flipping chips once at halfway point to ensure even cooking. I also rotated mine for more even cooking (optional but recommended). Note: thickness of slices will impact cooking time. Check at ~10 minute intervals during the second hour of cooking to ensure they aren't burning.
Remove once crisp and golden brown. Some may feel a little tender in the middle but take them out and let them rest for 10 minutes or so to crisp up before sampling. Serve immediately.
*I recommend organic sweet potatoes for taste and health reasons, since you don't peel off the skin where pesticides can reside. *Know that chips that are too thick in some spots may not crisp up all the way. They're still delicious, just not as crispy as the uniformly thin chips. It takes practice! *RECIPE UPDATED 1/26/14: I originally had the temperature at 200 degrees, but a few readers had trouble with the chips not crisping up properly. So I have retested with success, adjusting the temperature to 250 degrees. It still takes about 2 hours, but the low temperature allows them to get more evenly crispy. *Nutrition information is a rough estimate calculated without salt.