The nanoimprint lithography (NIL) of a hexagonal dot array pattern with 20 nm pitch was demonstrated using a tone reversal process. The dot array was formed by the self-assembled polystyrene-poly(dimethylsiloxane) (PS-PDMS) diblock copolymer. The dot pattern was transferred to a hole pattern on the imprint resist layer by a UV-NIL process. The hole pattern was filled with spin-on-glass (SOG). By removing the imprint resist matrix, the SOG dot pattern was formed as a final mask layer. The surface tension of the imprint resist was adjusted to achieve high-quality pattern transfer and demolding. The standard deviation of the diameter and pitch of the dot pattern suffered about 1% drop through the UV-NIL and tone reversal process.