1 μm double-stranded DNA molecules are immobilized between pairs of gold and pairs of platinum microelectrodes with gaps of 0.4 and 1 μm, respectively, and their electrical characteristics are determined under the application of constant and sinusoidal bias voltages. Due to their extremely high impedance for constant voltage bias, the samples of DNA are excellent insulators; however, their impedances show strong frequency dependence in the range of 10 Hz-7.5 MHz. Favorable response in the gold electrodes is attributed to the higher ability of DNA molecules to bridge the narrower gold electrode gaps in contrast to that in the wider platinum junctions. © 2008 American Institute of Physics.