In order to increase the separation rate of surface electrophoresis while preserving the resolution for large DNA chains, e.g., genomic DNA, the mobility and diffusion of Lambda DNA chains adsorbed on flat silicon substrate under an applied electric field, as a function of migration distance, ionic strength, and field intensity, were studied using laser fluorescence microscope. The mobility was found to follow a power law with the field intensity beyond a certain threshold. The detected DNA peak width was shown to be constant with migration distance, slightly smaller with stronger field intensity, but significantly decreased with higher ionic strength. The molecular dynamics simulation demonstrated that the peak width was strongly related with the conformation of DNA chains adsorbed onto surface. The results also implied that there was no diffusion of DNA during migration on surface. Therefore, the Nernst-Einstein relation is not valid in the surface electrophoresis and the separation rate could be improved without losing resolution by decreasing separation distance, increasing buffer concentration, and field intensity. The results indicate the fast separation of genomic DNA chains by surface electrophoresis is possible.