We report a saturating current characteristic of a 120 μm thick ZnO film and explore its X-ray sensing features. The film was deposited using a sol-gel spin coating technique. The film has a polycrystalline nature. Measurement of current-voltage (I–V) characteristic under dark condition shows two sublinear regions from 0 to 6.0 V and 6.0–8.0 V followed by a saturation region between 8.0 and 12.0 V bias voltage. The electrical resistivity in each region is found to be ∼1.0 × 1011, 1.2 × 1011 and 1.6 × 1011 Ω cm. The I–V characteristic was further recorded under X-ray irradiation. The current under the X-ray irradiation shows a linear region from 0 to 6.0 V followed by two sublinear regions from 6.0 to 8.0 V and 8.0–12.0 V with higher magnitude than the dark current. The resistivity in each region was found to decrease by ∼101 order of magnitude under X-ray. Analysis of X-ray sensing features reveals that the signal-to-noise ratio of the device is consistent between 3.0 and 12.0 V. The rise-time and fall-time are nearly 1 s. The device shows sublinear dose rate response between 0.015 and 0.293 Gy/s with a minimum sensitivity of 28.46 μC.Gy−1.cm−3 at 0.292 Gy/s. The device is also found to be visible-blind between 375 and 750 nm. The physical mechanism responsible for sublinear and saturating current characteristics have been explained based on retrapping and recombination of conduction electrons.