Hybridization of nucleic acids to microarrays is a crucial step for several biological and biomedical applications. However, the poor efficiency and resulting long incubation times are major drawbacks. In addition to diffusion limitation, back hybridization to complementary strands in solution is shown to be an important cause of the low efficiency. In this paper, repeated denaturing in an integrated device has been investigated in order to increase the efficiency of microarray hybridization. The sample solution is circulated from the microarray chamber over a denaturing zone and back in a closed loop. In addition to the improved binding rate due to flow, repeated denaturing significantly increases the total amount of molecules bound. Our results demonstrate that cyclic repeated denaturing improves the efficiency of hybridization by up to an order of magnitude over a broad range of concentrations studied (1 pM to 100 nM).