We report the electrical behavior of undoped zinc oxide thin-film transistors (TFTs) fabricated by low-temperature chemical spray pyrolysis. An aerosol system utilizing aerodynamic focusing was used to deposit the ZnO. Polycrystalline films were subsequently formed by annealing at the relatively low temperature of 140°C. The saturation mobility of the TFTs was 2 cm2/Vs, which is the highest reported for undoped ZnO TFTs manufactured below 150°C. The devices also had an on/off ratio of 104 and a threshold voltage of -3.5 V. These values were found to depend reversibly on measurement conditions.