Nitrogen (N) is a potential acceptor dopant making a p-type semiconductor of Ga2O3. Considering highly compensative nature of metal oxides, however, high dopant concentration with low defect density is essential to the acceptor activation. In this study, we employed nitric oxide (NO) as a source of O and N during pulsed-laser deposition (PLD) of β-Ga2O3:N films. The N concentration of the films prepared on β-Ga2O3 (100) substrates was found to be ∼1021 cm-3, which is the highest ever attained. Despite of such a high concentration, the films showed high crystallinity. Moreover, both of N concentration and crystallinity of the films grown under NO plasma increased with increasing growth temperature. As a result, highly insulating properties were obtained for films grown under NO plasma. These results suggest that PLD under NO plasma is effective for high concentration N-doping into device-grade β-Ga2O3 films.