In a floating gate memory cell including a floating gate separated from an active region by a tunnel isolation region, a first one of the active region and the floating gate comprises a portion that protrudes towards a second one of the active region and the floating gate. In some embodiments, the protruding portion tapers toward the second one of the active region and the floating gate. The tunnel insulation layer may be narrowed at the protruding portion. Protruding portions may be formed on both the floating gate and the active region.