  Each satellite of the Gravitational wave high-energy Electromagnetic
Counterpart All-sky Monitor (GECAM, mission) consists of 25 SiPM based
gamma-ray detectors (GRDs). Although SiPM based GRD has merits of compact size
and low bias-voltage, the drift of the SiPM gain with temperature is a severe
problem for GRD performance. An adaptive voltage supply source was designed to
automatically adjust the SiPM bias voltage to compensate the temperature
effects and keep the gain stable. This approach has been proved to be effective
during both the on-ground and in-flight tests. The in-flight measured variation
of the SiPM gain is within 2%. To reduce the gain non-uniformity of GRDs, an
iterative bias voltage adjustment approach is proposed and implemented. The
gain non-uniformity is reduced from 17% to 0.6%. In this paper, the gain
stabilization and consistency correction approach are presented and discussed
in detail.
