Preheat oven to 375 degrees and line two baking sheets with parchment paper.
Bring a large pot of water to a boil.
Peel squash and slice in half lengthwise. Scoop out any seeds in the base of the squash.Using a very sharp knife (or a mandolin if you have it) thinly slice the squash. The thinner, the better. Mine were probably about 1/8 of an inch thick.
Once sliced, boil (in batches) for 1-2 minutes. Remove from water and lay flat in a single layer on a paper towel to dry.
Pat completely dry and then transfer to baking sheet, making sure the slices don't overlap at all.
Brush with olive oil to coat and sprinkle generously with salt and pepper.
Sprinkle chopped rosemary on top and bake for 20 minutes, checking frequently after 10 minutes to make sure they don't burn. If your slices are thinner than 1/8 of an inch, they won't need to bake as long.
Remove from oven once they start to brown and crisp up and immediately sprinkle with more salt.
Recipe by Running to the Kitchen at http://www.runningtothekitchen.com/2012/10/crispy-baked-butternut-squash-chips/