In semiconductor manufacturing, it is a key to ensure reliability of the produced devices. The population's reliability level is demonstrated by means of a burnâin study (that is investigating a large number of devices under realâlife stress conditions for product relevant fails). Burnâin settings are based on the lifetime distribution of early fails. Typically, it is modelled as a Weibull distribution Wb(a,b) with scale parameter aâ>â0 and shape parameter bâââ(0,1) motivated by a decreasing failure rate within the devices' early life. Depending on the applied burnâin scheme, the Weibull parameters have to be estimated from timeâtoâfailure and discrete failure count data, respectively. In this paper, we present advanced Bayesian estimation models for the Weibull distribution handling both data situations. First, a simplified conjugate approach using gammaâhistogramâbeta priors is presented. Further, according to the paper's main focus, an extended Bayesian concept for assessing Weibull early life failure distributions is highlighted. It is characterized by a Dirichlet prior distribution applied to the lifetime function of early fails. The proposed model simplifies the incorporation of engineering prior knowledge. Moreover, it can be extended to both discrete failure and timeâtoâfailure burnâin data. The joint posterior distribution, Bayesian estimators and compounded and joint credible regions are derived by means of Monte Carlo simulation. The principle of Bayesian learning allows to update the Weibull early life failure distribution whenever new failure data become available. Therefore, burnâin settings can dynamically be adapted improving the efficiency of burnâin. Copyright Š 2014 John Wiley & Sons, Ltd.