Control over the placement of stretched deoxyribonucleic acid (DNA) molecules in a microfluidic system is a critical requirement for molecular nanotechnology. A technique is developed where a large number of DNA molecules can be immobilized specifically at one end to the electrode tip and stretched in a microchannel using high frequency ac fields. λ-DNA molecules are immobilized and stretched using 100kHz ac fields in a 100μm wide and 75μm deep Si microchannel. Using a floating electrode in between two biased electrodes, stretched T2 DNA molecules are immobilized across a 5μm wide electrode gap by electric field and hydrodynamic flow.