The primary FORMOSAT-3 mission is to launch a constellation of six micro-satellites into Low-Earth Orbit (LEO) in altitude range 700~800 km
to collect atmospheric data for weather prediction, atmospheric studies,
space weather monitoring and geodetic research. Six satellites are
operating separately after launch and functioning normally during the
early-orbit checkout phase. The major objectives of this paper are to study flight temperature trending data and major factors that may affect the temperature variations of satellite components in early orbit checkout phase.Besides, the temperature comparisons of the critical components among the six satellites are also performed. The temperature behaviors of six satellites are similar due to the same configuration and thermal environments. The temperatures of satellite components are all well controlled within their operating temperature limits except some cases caused by different power dissipation and operation scenario. All the details are described in this paper.