A field emission diode array with a novel nanometer scale silicon gap in a separation by implantation oxygen structure was fabricated using the thin film stress that had been generated during high-temperature annealing and cooling. In this work, an interelectrode gap ranging from 20 to 100 nm was obtained depending on the width of the pattern when the patterned wafer was cooled after annealing at 1050 degrees C for 1 h in N-2 ambient. The parameters for determining the gap size were identified, and the crystal orientation dependency in forming the gaps was clarified. The proposed nanogap formation technique is very simple and applicable to a field emission (FEA) with a short interelectrode distance. The fabricated FEA exhibited a turn on voltage of 25 V and an emission current of 6 mu A per tip at 35 V.