A high density anti-fuse cell can be built at the cross points of two perpendicular interconnect lines, such as active region lines, active and polysilicon lines, active and metal lines, or polysilicon and metal lines. The cell size can be very small. At least one of the anti-fuse cells have a thin oxide fabricated before, after, or between a diode in at least one contact holes at the cross points of the interconnect lines. The thin oxide of the anti-fuse cells at the cross points can be selected for rupture by applying supply voltages in the two perpendicular lines. In some embodiments, a diode can be created after thin oxide is ruptured so that explicitly fabricating a diode or opening a contact hole at the cross-point may not be necessary.