Reproducible and stable p-type ZnO thin films have been prepared by the N-Al codoping method. Secondary ion mass spectroscopy measurements demonstrate that N and Al are incorporated into ZnO. The resistivity, carrier concentration, and Hall mobility are typically of 50-100 Omega cm, 1 x 10(17)-8 x 10(17) cm(-3), and 0.1-0.6 cm(2)/Vs, respectively, for the N-Al codoped p-type ZnO films. Hall measurement, X-ray diffraction, and optical transmission were carried out to investigate the changes of the properties with the storage period. Results show that the p-type characteristics of the N-Al codoped ZnO films are of acceptable reproducibility and stability. In addition, the N-Al codoped p-type ZnO films have good crystallinity and optical quality. The properties are time independent. (c) 2006 Springer Science + Business Media, Inc.