To investigate their memory behaviours, single-walled carbon nanotubes (SWCNTs) were embedded in the floating gate of a hybrid metal–insulator–semiconductor structure using layer-by-layer deposition, and polymethylmethacrylate (PMMA) as the dielectric. Unlike longer SWCNT-based structures, shortened SWCNTs were shown to exhibit reliable and large memory windows by virtue of a better encapsulation which reduces charge leakage. The capacitance–voltage characteristics of the devices were consistent with electron injection into the SWCNT charge storage elements (in the floating) from the top electrode through the PMMA, using localized defects and crossing the PMMA energy barrier. In terms of material formulation, a combination of SWCNTs dispersed in sodium dodecyl sulfate and polyethyleneimine used as charge storage elements in the floating gate was shown to lead to repeatable and reliable memory characteristics. Fast switching and very large memory windows (~7 V) exhibiting high charge density (2.6 × 1012 cm−2) and charge retention in excess of ~76% were achieved under a ±10 V sweep voltage range. These results suggest that SWCNTs could lead to improved memory behaviour with the potential for application in plastic electronics.