Gate-oxide and inter-gate-oxide defects in floating-gate transistors and flash memories, the number of which has been minimized but is still not zero, have been examined extensively. Gate-oxide defects are due to 0.1 μm size octahedral void pits at the Si surface. They are originally grown-in defects in the Si crystal and appear as surface pits when they are truncated at the surface when wafers are sliced and polished. On the other hand, inter-gate oxide defects are due to polygonal-shaped voids at the poly-silicon grain boundary. These defects are produced as a negative crystal in the crystallization process of amorphous Si during annealing. Methods for eliminating the above defects are suggested.