Autism Spectrum Disorders Semipostal Stamp Act of 2012 - Requires the U.S. Postal Service (USPS) to issue a semipostal for a five-year period, the proceeds of which shall be transferred to: (1) the National Institutes of Health (NIH) for research into autism spectrum disorders, and (2) the Administration on Developmental Disabilities for new demonstration projects that are projects of national significance described in the Developmental Disabilities Assistance and Bill of Rights Act of 2000 and that are designed to ensure that individuals with autism spectrum disorders have the opportunity to achieve their fullest potential.