Method of ssDNA preparing in single-round PCR for microarray application is described. The approach is exemplified on genotyping of DARC gene. It is opposed to two-round PCR that consists of separate symmethric and asymmethric stages. Implementation of reaction in single round is achieved by means of low-melt excess internal primer application. The primer do not anneal during symmethric stage but after decreasing of annealing temperature on asymmethric stage. The results indicate effective oligonucleotide microarray genotyping. The approach reduces time requirements and risk of contamination.