The use of predictive biomarkers can help to improve therapeutic options for the individual cancer patient. For the treatment of colon cancer patients with anti-EGFR-based drugs, the KRAS mutation status has to be determined to pre-select responders that will benefit from this medication. Amongst others, array-based tests have been established for profiling of the KRAS mutation status. Within this article we describe an on-chip hybridization technique to screen therapeutic relevant KRAS codon 12 mutations. The DNA chip-based platform enables the reliable discrimination of selected mutations by allele-specific hybridization. Here, silver deposits represent robust endpoint signals that allow for a simple naked eye rating. With the here presented assay concept a precise identification of heterozygous and homozygous KRAS mutations, even against a background of up to 95% wild-type DNA, was realizable. The applicability of the test was successfully proven for various cancer cell lines as well as clinical tumour samples. Thus, the chip-based DNA hybridization technique seems to be a promising tool for KRAS mutation analysis to further improve personalized cancer treatment.