Abstract: A thermo sensor assembled to a unit under test has a metal plate, a passive component, and a package. The metal plate has an installation socket and at least one cable tray. The installation socket has a flat conducting base. The passive component has a main body mounted in the installation socket and at least one cable respectively mounted in the at least one cable tray and electrically connected to both the main body and the metal plate. The package integrally encapsulates the metal plate and the passive component. The conducting base is revealed outside the package and directly contacts the unit under test. Therefore, the passive component has a rapid and precise response to heat, and the thermo sensor can be applied to various positions and can get accurate readings without being interfered by the external environment.