The use of Au/SiO_x interfaces for the investigation of DNA hybridization using electrochemical impedance spectroscopy (EIS) and surface plasmon resonance (SPR) simultaneously is demonstrated. Standard glass chemistry was used to link single-stranded DNA (ss-DNA) on aldehyde-terminated Au/SiO_x interfaces. The layer thickness and amount of grafted oligonucleotides (ODNs) were calculated from SPR on the basis of a multilayer system of glass/Ti/Au/SiO_x/grafted molecule. Capacitance and resistance values of the modified interface before and after hybridization were calculated from EIS data using an equivalent circuit and allowed the affinity rate constant, K_A = 4.07 × 10⁵ M^-1, to be determined. The EIS results were comparable to those obtained by SPR hybridization kinetics recorded in parallel.