Embodiments of the present invention provide devices methods for sequencing DNA using arrays of reaction regions containing sensors to monitor changes in solutions or bound molecules contained in the reaction regions. Additional embodiments provide devices and methods for sequencing DNA using arrays of reaction regions that allow for optical monitoring of solutions in the reaction regions. Chemical amplification schemes that allow DNA to be sequenced in which multiple nucleotide addition reactions are performed to detect the incorporation of a base are disclosed. By sequencing DNA using parallel reactions contained in large arrays, DNA can be rapidly sequenced.