Entropic trapping of long DNA was demonstrated in an artificial channel, fabricated by-silicon based lithography and etching techniques. This channel-consisted of alternating thick and thin. regions, where the thickness of the thin region was as small as 90 nm. The electrophoretic mobility of long DNA molecules in this channel was measured as a function of the applied electric field. Because the radius of gyration of DNA used was much larger than the thin gap, DNA molecules were trapped when they moved from the thick to the thin region, This trapping determined the mobility of DNA in the system. Surprisingly, longer DNA molecules moved faster than shorter DNA molecules in the channel. This may be due to the fact that a, larger DNA. molecule has a better: chance of escaping entropic traps because of the larger contact area with the thin slit; This device could enable fast: manipulation and separation of long polymers.