In this paper, we have studied the effect of oxidation temperatures on the quality and reliability of the ultrathin oxide. It has been observed that for the same oxide thickness, MOS capacitors exhibit a higher leakage current and lower breakdown voltage when the oxide is grown at a lower temperature. We have correlated this increase in leakage current to the effective electron tunnel mass parameter (m*) and shown that with reduction in the oxidation temperature, the value of m* reduces, signifying the presence of more defects and an increase in defect-assisted tunneling. Also, voltage ramp tests have been carried out to study the time to breakdown (tBD) and the shape factor (β) of the Weibull distribution for these devices. It is found that lowering the oxidation temperature adversely affects both of these parameters. © 2005 Elsevier B.V. All rights reserved.