This article presents a trial for deriving a thermal transfer model of a thermostat housing a heat source generating several watts and achieving high temperature stabilization. It is intended for investigating the open-loop linearity of operational amplifiers labeled as high precision or low noise and their noise characteristics. This thermostat is built up with a double-jacket constructed with a copper plate of 10 mm thickness and an approach of deriving a lumped parameter model to each jacket on the temperature control is presented. The temperature stability of the order of3×10−5°C per 1°C temperature change in the air outside in 1 h is realized in the inner jacket. The linearity is measurable and it is clarified that amplifiers are classified into three groups. ©1997 American Institute of Physics.