Use a sharp knife or mandolin slicer to cut sweet potato into paper-thin slices. Pour slices into a bowl and carefully coat in oil and lemon juice by rubbing gently. Add dried rosemary and salt then toss.
Spread coated slices on dehydrator trays without touching each other. Dehydrate on 165°F (74°C) for 10 hours or until dry and crispy. If they need extra time put them in for 2 hour increments. Rotate trays as necessary to dry potato chips equally.
Turn off the dehydrator, and set aside to cool. Store crispy potato chips in an airtight bag or container.