Gate length (L-G) effects for program/erase (P/E) efficiency are investigated in a gate-all-around (GAA) SONOS structure. The experimental results show that PIE characteristics become worse at a shorter L-G, and this trend is verified with numerical simulation. The down-scaling of L-G gives rise to a change in the electric field in tunneling oxide and blocking oxide in the GAA-SONOS structure. For PIE efficiency, these results reveal that the fringing field via a low-k dielectric medium, which encapsulates a gate electrode as an inter-layer dielectric, favorably enhances the electric field of tunneling oxide. It also reduces the electric field of blocking oxide. Additionally, it is found that the electric field of tunneling and blocking oxide becomes more sensitive to the permittivity of the inter-layer dielectric as L-G is more shortened. (C) 2012 Elsevier Ltd. All rights reserved.