The passivation layers in the thermal inkjet printhead are not only crucial for the life time, but also for thermal characteristics of the thermal printhead device. In this paper, therefore, the experimental and simulated results are presented to investigate the effects of the passivation layers on the bubble onset characteristics and temperature distribution. The experiments were carried out by use of the open pool test to measure the bubble onset voltage. The effects of the different passivation layer structures and the loop resistance on the bubble onset voltage are studied. Moreover, a one-dimensional heat transfer model is employed in this paper to understand the temperature distribution across the device structure.