This paper reports measurements that characterize the immobilization of 48 kilobase-pair lambda DNA onto lifted-off microelectrodes by high-voltage and high-frequency dielectrophoresis. Measurements of voltage- and frequency-dependent immobilization of DNA onto microelectrodes by dielectrophoresis show significant reduction in the response as the frequency increases from 200 kHz to 1 MHz or decreases from 200 kHz to 100 kHz and also as the electric field is lower or higher than 0.4 Vp-p/m. We found that the immobilization and elongation of the DNA molecules is restricted by the geometry of the gap, and that by decreasing the electrode gap size, the DNA molecules have less chance for both immobilization and stretching. The produced electrodes with both random microscopic peaks and modified smooth edges are utilized to show the effect of electrode edge roughness. The results imply that more DNA molecules can be immobilized by microelectrodes having rough edges.