The extension of chromosomal DNA is a key technique in high-resolution gene location such as extended fibre fluorescent in situ hybridization. In this paper, we propose a new micro-device designed for on-chip integration of three functions, (1) positioning of cells, (2) extending chromosomal DNA from the cells, and (3) anchoring the extended DNA fibres. The device has a flow chamber equipped with (a) multi-phase electrodes to create electroosmotic flow (EOF) of variable direction, (b) a set of micro-fabricated pocket-like structures for cell positioning, and (c) a micro-pillar array whose surface is chemically modified to anchor DNA fibres. First, unidirectional EOF is induced, by which cells are carried into the micro-pockets and positioned, one cell at each pocket. After rupturing the cells, chromosomal DNA from each cell is hydrodynamically extended by EOF. When the EOF direction is rotated through 90°, the fibres are made to contact with the pillars to be anchored. Because the velocity of the EOF is controllable, the breakage of DNA during the process can be minimized. Thus immobilized DNA fibres are suspended a few microns above the surface, allowing free access of probe molecules.