On each chestnut's sharp end, cut a "X" using a knife.
After that, put the nuts on a microwave-safe pan and heat them for one minute intervals, checking to see if the outer shell is beginning to peel back somewhat where you scored (This usually takes 3-4 minutes, depending on your microwave).
As soon as you can handle them comfortably, peel off the shell. When chestnuts are hot, peeling is easy.