  The gain of SiPMs depends both on bias voltage and on temperature. For stable
operations, both need to be kept constant. In an ILC calorimeter with millions
of channels, this is a challenging task. It is, therefore, desirable to
compensate for temperature variations by automatically readjusting the bias
voltage. We have designed a bias voltage regulator board to achieve this task.
We anticipate an uncertainty on the gain stability at the level of $< 1\%$.
First, we present measurements of the gain dependence on temperature and bias
voltage for several SiPMs from three different manufacturers and determine
their dV/dT dependence. Next, we demonstrate the performance of the gain
stability with the bias voltage regulator test board on four SiPMs.
