We demonstrate memory effect of pentacene-based field-effect transistors (FETs) in which CdSe/ZnS colloidal nano-dots (NDs) are embedded. The colloidal NDs were dispersed in chloroform, and spread over a water surface to form monolayer of NDs. Then, they were transferred onto a 30-nm-thick poly(methyl methacrylate) (PMMA) surface by horizontal lifting method, and a 30-nm-thick pentacene film was deposited as an active layer to fabricate FETs. The threshold voltage ( V th) was shifted by ∼10 V after a writing voltage of 70–100 V was applied to the gate electrode of the memory-FETs. On the other hand, such a large shift of V th was not observed for reference pentacene-FETs without NDs. We consider that the large shift of V th is due to electrons trapped in the NDs at the interface of pentacene and PMMA layers.