This study investigated carrier compensation induced by thermal annealing in sputtered ZnO:Al (Al2O3: 0.25, 0.5, 1.0, and 2.0 wt %) films. The films were post-annealed in a N-2 atmosphere at low (1 x 10(-23) atm) and high (1 x 10(-4) atm) oxygen partial pressures (P-O2). In ZnO:Al films with low Al contents (i.e., 0.25 wt %), the carrier density (n) began to decrease at annealing temperatures (T-a) of 600 degrees C at low P-O2. At higher P-O2 and/or Al contents, n values began to decrease significantly at lower T-a (ca. 400 degrees C). In addition, Zn became desorbed from the films during heating in a high vacuum (i.e., <1 x 10(-7) Pa). These results suggest the following: (i) Zn interstitials and Zn vacancies are created in the ZnO lattice during post-annealing treatments, thereby leading to carrier compensation by acceptor-type Zn vacancies; (ii) The compensation behavior is significantly enhanced for ZnO:Al films with high Al contents.